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Basic PSU buyers guide:

I have seen enough conversation, (and whats worse, misunderstanding) about PSU's around here, that I thought that I would try writing a brief guide for those of you that are either upgrading, or are building a completely new system. Keep in mind that this guide is NOT comprehensive, and that if you have any additional questions that you should post them in the forum (thats why you joined right... to ask questions instead of just read
).

Special thanks to Phaedrus2129 for his great in depth explanations/discussions of terms and manufacturers that you'll find scattered throughout the guide, and to shinji2k for his great suggestions for helping make this a better guide.


PSU Basics:


Everyone knows that a PSU is rated in terms of watts. The question is always "will this ____ PSU be enough for my system?". The thing is, not all companies rate their PSU's the same, and in that way, not all Watts are created equal.

In reality, as long as the PSU has enough amperage on the 12v rail, it should easily have enough wattage for whatever it is that you might need. The reason that I say this, is that the two components that pull the most power (CPU and GPU), both run off of the 12v "rail" of the PSU (the part that puts out 12v, rather than the 5v or 3v rails).

Most companies will list how much amperage the PSU has on the 12v rail on the sticker on the side of the PSU. If not, then you just have to do some simple math. Amps = watts/volts, so its easy enough to figure that out. For instance, my Antec Earthwatts 430w PSU has 360w on the 12v rail, so you can see how 360w/12v = 30amps.



Now, for where things are really misunderstood. I have seen a lot of posts that talk about a PSU having so many 12v rails with 18amps, and they simply add them together for the total amperage of the unit. This is not the way that works. You must do it the same way that we did before, which is to find the total amount of power available to the 12v rails as a whole (almost all multi-rail systems are actually just a split single rail), and do the same math.

For instance, my 430 is listed as having two 17amp 12v rails, which would give me 34 amps if you just added them together. The trick is that while those rails function semi-independently, the total that is drawn from them cannot be greater than the 360w that was stated before, which is why the real amperage is 30amps, not 34.

In general, this is how it breaks down as far as wattage and amperage for different types of builds. Though obviously this is more to give you a basic idea of what you should be looking at, than being a definitively guide to which PSU to buy.

Midrange Single card rigs 300-400w is fine, 24-32amps

Performance single card rigs 400-600w, 32-40 amps

Performance multi-card rigs 600-1Kw, 40-60amps

HERE is the best PSU calculator that I know of. Notice that it will tell you the wattage that you need, but will also tell you about this whole "amperage thing" that I keep talking about. Between this forum and that calculator, I think you should get a pretty good idea of what your system will need.

A good quality PSU is also important:

The PSU plays more of a part than most people might think. The PSU is what supplies the power for everything (I know, obvious, but hear me out). If the PSU is of poor quality, it can provide very "dirty" power to the components (power that is bouncing around a lot in the acceptable range). This can hamper your OC (because the CPU isn't getting a clean, stable supply of power, its jumping all over the place), as well as potentially damage components. In fact, a bad PSU is one of the easiest ways to loose hardware. If it for some reason spikes, it could easily zap everything in your computer.

*Case in point: One time I helped an OCN member out that had sporadically unstable OC's... turns out it was the fact that his computer was plugged into the same circuit as his refrigerator, and apparently that caused the power to fluctuate enough that it made the OC unstable. The problem stopped when he put the computer on another circuit.

How to Find a Quality PSU:

There is no quick and easy way to know if the PSU is high quality, or a waste of money. There are some things you can do to help you make a more informed choice however. Always try to find out as much about the PSU you are looking at before you buy. When looking at reviews, make sure that you look to make sure the power is stable ( more info HERE), and the that rails are actually putting out what they are supposed to put out (more info HERE).

In other words, put as much effort into choosing a PSU as you do the other major components in your computer (Motherboard, CPU, GPU, etc). They are not all created equal.

A few good resources for PSU reviews and information include: jonnyguru, Hardwaresecrets , and [H]ardOCP. Make sure you check them out, as the PSU is really the backbone of the system.

I think this is also a good place to mention the fact that having at LEAST a good surge protector. Even if you have a good PSU, a power surge can take it, and usually your motherboard out in just a few seconds (Its most common to have a surge take out those two components, more specifically, the MOSFETS or other caps on the motherboard). Having a good surge protector, or even better, a UPS will help make sure that your computer lasts as long as it should, as well as making it more stable for even better OC's.

Some good manufacturers of PSU's (aka, ones that have a good reputation):

Corsair, PC Power & Cooling, Antec, Seasonic, Delta, OCZ and Thermaltake. Of course there are others, but here in the states, those are some of the better known manufacturers. The manufacturer is not itself a guarantee that the PSU will be good quality, but the odds are more in your favor. As a very general rule of thumb, look at the efficiency of the PSU that you're looking at. If the PSU is very efficient (better than 75%) then its probably at least decent (it takes good components to make an efficient PSU, the ones with low efficiency are often not that great of quality).

To better understand what efficiency and the 80+ certification mean, click HERE.

* like I said before, this is not the best way to find out if the PSU is good, but in the lack of other things like reviews or other additional information, its better than a shot in the dark

Other than that, just look for the PSU that has the right connections for what you need (note: Modular PSU's are convenient, but there has been some question of the reliability of the connections , especially after repeatedly taking them apart, so just be aware of that. In general it is a non issue though). Sleeving is also nice, and not only helps out with the aesthetics of the case, but makes cable management easier, although its not really essential.

Final notes:

A dying PSU will usually just cause the computer to turn off at random, usually without warning. This can also be caused by the PSU overheating. A PSU that is underpowered will usually make itself known when the PSU is under the most load (stressing both the CPU and the GPU at the same time.... like intense gaming or benchmarks).

A PSU can be bad, even if the fans and lights of the computer turn on. That is another common thing that I see. People will say that the PSU can't be bad, because the fans spin... that just isn't true. A fan will operate with huge differences in voltage... a CPU will not.

Hopefully this helps clear things up a bit for some of you. I know that most of you probably knew all of this, but I think enough will find this useful as it is, and it will be part of a more comprehensive OC guide that I am working on in conjunction with thlnk3r and Joe. Because we all know that OCin isn't just about the CPU, the rest of the system also comes into play.

The OCin Guide is in now my Signature, make sure you check it out if you're into PhII's or would just like to understand how they OC. Its a good read if I can say that about my own work
.

Cheers!
LL
 

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nice guide, thats way i use apevia power supplies, they are for the extreme gamer since my extreme edition pentium 4 made the apevia go pop.
 

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Sticky ! Nice guide man , helped me clear up some uncertainties about PSU !
 

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Yep it's good for sure, so +rep coming your way. Also highlights that PSU specs can be misleading.

Assume you pulled 17A from one of your 12V rails, that's 17 * 12 = 204W. 360W - 204W = 156W. 156W / 12V = 13A. 13A is what's left over on the other rail. So, basically if one rail is fully loaded, the other one is left "lopsided", so to speak. A more "honest" PSU would have enough juice to allow each rail to be fully loaded.

It'd be nice if systems like ESA could show this sort of thing on a gauge - the relative loads on each of the rails.
 
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My claws fix anything
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Discussion Starter #10
How do you look for it?

Well most reputable manufacturers will tell you the efficiency of the PSU in the specifications. Usually if they don't tell you the efficiency, you can assume that it is not all that great (maybe 65-70% for instance).

Here is a typical newegg screenshot with the efficiency highlighted.



Another way to tell the efficiency is the 80+ rating that PSU's can now be certified with. The 80+ Ratings are simple, they are rated as 80+, 80+ Bronze, 80+ Silver or 80+Gold. And just like you would expect, the cooler the name is the more efficient the PSU.

I would read through THIS to give you the specifics to help you understand better what the ratings mean.

Hope that helps
.
LL
 

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Quote:
If the PSU is very efficient (better than 75%) then its probably at least decent (it takes good components to make an efficient PSU, the ones with low efficiency are often not that great of quality).
This is simply not true. Low efficiency is a sign of an older design. It is not indicative of a poorly performing or poorly built PSU. There are plenty of examples of less efficient, older PSUs being amazing and very efficient units being crap. In fact, in the race for the highest efficiency possible a few designs sacrifice performance and tweak for efficiency. Efficiency is not a reliable indicator of quality and unfortunately there is no easy method for differentiating a good PSU from a bad PSU at a glance. 80plus certification is also not a reliable way of determining quality. They only test at 23C which is an unrealistic operating temp for the inside of your case and they only test for efficiency. Ripple could be off the charts frying your components or there could be terrible build quality, but as long as it is meets efficiency requirements it is 80plus certified. You can't even rely on good brands/manufacturers since nearly all of them are not consistently good. Corsair, PC Power & Cooling, Antec and Seasonic all have made/sold units that are only average performers with slightly disappointing build quality (but not bad build quality). Delta as a manufacturer is very good due to their robotic assembly line/soldering, but they have made some pretty unimpressive stuff at the request of the companies they sell units to. OCZ likes to sell barely good enough units, with the occasional junk (GXS 850W, 1010W). It certainly isn't fair to group them with the others. Thermaltake only sells one line of good units (Toughpower), everything else is either mediocre or junk especially since they are relying on HEC a lot recently.

I guess my point is the fatal flaw of all of these types of guides is trying to oversimplify. There are too many manufacturers, with too many designs and too little industry regulation. There are far too many examples of inflated ratings or poor build quality even from supposed trusted companies. Unfortunately PSUs aren't cut and dry, black and white. There are way too many shades of gray. If you see a PSU that is interesting, look for a well done review. If one of the handful of trusted reviewers hasn't looked at a particular PSU, ask around/look for more info. More often than not the same PSU design is sold by multiple companies, so there are very few unknown PSUs even if your particular one hasn't been reviewed. To make this guide better you need to add links to trusted reviewers like jonnyGURU, [H] and hardwaresecrets and to other places where people can learn more about PSUs. You also need to point out what makes a PSU good, efficiency being one of the less important things (performance characteristics, build quality, price/performance). Maybe you could pick out a few of your favorites for each power level to give people an idea of where to start.

Oh, I almost forgot, that part about modular connectors being unreliable is a non-issue. Of course they will wear out if you repeatedly unplug them, but the same goes for the connectors going to your components. As long as you don't mess with them constantly for years, there won't be any reliability problems.
 

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Shinji, have you read my more recent guides? You can't generalize about PSUs for sure, but you can educate people about what the terms thrown about in reviews actually mean.
 

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Quote:


Originally Posted by Phaedrus2129
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Shinji, have you read my more recent guides? You can't generalize about PSUs for sure, but you can educate people about what the terms thrown about in reviews actually mean.

Yours are just fine. There's a difficult balance between generalizations and too much info, it's hard to make a great guide that is useful and but not boring or too much to read. I hate sounding negative since I know the OP put a lot of work into this one, hopefully he can add some more to it if he still cared about this. I'm not sure how I've missed it for this long. As for yours, you have plenty of links to important info/reviews for people interested in learning more, enough basic info to get started with the various ripple/voltage/efficiency threads and you've broken up your analysis of each major company to separate threads to keep you from having one giant guide that most people would find overwhelming. I see you have yet to work on a general buyers guide/recommended type thread, do you have any plans for one?
 

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Not really. Closest I've come is a list of all the Corsair PSUs, with better value PSUs (either equivalent or better for the same money or less, or much better for slightly more).
 

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My claws fix anything
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Discussion Starter #15
Thanks for the input guys, I never claimed to be an expert on PSU's but it helps to have a few of you around.

Actually, when I put this together, it was for something else entirely (PhII OCin guide), and I only wrote it because there really wasn't anything like it that I could find in this section of the forum. I know that it was a simplification but it was more to get people to understand the basics of PSU's without getting them to overwhelmed by the rest of the guide that I was writing.

I know that you can't really make any broad sweeping statements about PSU's any more than you can about any other PC component. If there was one or two rules of thumb that you wished EVERY new member to the forum knew about PSU's... what would it be? I chose that wattages are not everything, and pointed out some decent manufacturers.

I appreciate you trying not to be to hard on this, as I did put a decent amount of time into it. However, I am completely open to adding more links so people can find addition information if they so desire it (I did it for the other 4 parts of my guide, but for some reason spaced it here). And I really don't know why I didn't put a link to Johnnygurus in here, in fact I'll put it in right now.

I'll try to make it more clear, and in the meantime feel free to post up some links for me to include in the guide. And finally, after all this time I'm getting some feedback
.
 

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I hope I didn't sound too negative. It's difficult for me to be critical without seeming rude or offensive. If you can clear up some of those issues and add links to further reading and reviews it would certainly improve this guide. Some useful links would be the review sections of Hardwaresecrets.com, [H]ardOCP.com and jonnyGURU.com. The forums at jonnyGURU.com are also quite useful either by reading stickies or just searching for info on various PSUs.

As for tips I'd like people to know... Read reviews, but not just any reviews. Hardwaresecrets has quite a few good articles on top of reviews like Why 99% of Power Supply Reviews Are Wrong, Everything You Need to Know About Power Supply Protections, Understanding the 80 Plus Certification and Anatomy of Switching Power Supplies to name a few.
 

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My claws fix anything
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Discussion Starter #17
Quote:


Originally Posted by shinji2k
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I hope I didn't sound too negative. It's difficult for me to be critical without seeming rude or offensive. If you can clear up some of those issues and add links to further reading and reviews it would certainly improve this guide. Some useful links would be the review sections of Hardwaresecrets.com, [H]ardOCP.com and jonnyGURU.com. The forums at jonnyGURU.com are also quite useful either by reading stickies or just searching for info on various PSUs.

As for tips I'd like people to know... Read reviews, but not just any reviews. Hardwaresecrets has quite a few good articles on top of reviews like Why 99% of Power Supply Reviews Are Wrong, Everything You Need to Know About Power Supply Protections, Understanding the 80 Plus Certification and Anatomy of Switching Power Supplies to name a few.

I understand, its difficult to offer improvements without offending people. I think you did just fine.

Like I said, I only wrote this because there really didn't seem to be anything like it out there at the time. And since I posted it I have been super busy with school and life, and havn't had the time to update it until now.

Also, if I might ask, the question I had about if there was one or two main things that you wish EVERYONE on the forum knew about PSU's was not a rhetorical one. I really am interested in what you would want everyone to know, and I'll see if I can incorporate it.

I will update the article more tomorrow, as this is the first time I have been able to see my wife all day, and I think she would like to see me.

Thanks again.
 

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Quote:


Originally Posted by logan
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Also, if I might ask, the question I had about if there was one or two main things that you wish EVERYONE on the forum knew about PSU's was not a rhetorical one. I really am interested in what you would want everyone to know, and I'll see if I can incorporate it.

Hm... PSUs aren't just a magic box that powers your computer. Few people have a practical understanding of electronics or what goes into making a good PSU and many PSU manufacturers/resellers have little issue taking advantage of this. Just as you would read well done reviews on a motherboard or video card you are looking to purchase, find out as much as you can about PSUs you are interested in purchasing from one of the trusted reviewers I linked to. They are arguably the most important component of your computer, so you should try to budget for one that is of acceptable quality. I'm not going to tell you that you have to go buy the best PSU you can since you will likely not see any difference from one that is good but still affordable, but skimping on a PSU is the last thing you should do.

I'm not too good at this.
 

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Originally Posted by inmate
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How do you look for efficiency? Really good article!!!

Look here: http://www.80plus.org/manu/psu/psu_join.aspx

However these results are really slanted in favor of the PSU and here is why.

Quote:


As is specified in IEC 62301, the tests shall be carried out in a room that has an air speed close to
the UUT of ≤ 0.5 m/s, and the ambient temperature shall be maintained at 23°C ± 5°C
throughout the test.

Source

Really? 23°C ±5°C? Really? So the temp in the room could be 18C, boy would the PSU be loving that. That range is absurd to me because as a calibration technician my lab had a spec of 22°C ±1°C. What about the poor PSU's who have handicapped results because they had to be tested in 28°C temps? Results cannot be taken completely at face value. Also, did the companies submit a ringer to 80Plus to be tested? Did they send the most efficient PSU out of 20 tested at the factory?...not that anyone would do that....right?

Temperature plays a large part in how efficient a PSU is....as temps go up efficiency slowly slides down. Some PSU's are affected very little by temperate while other PSU's have their efficiency take a nose dive by as little as a 5°C rise in temp.

For efficiency results to mean anything the testing must be done in a temperature that represents the environment that the PSU will be used in.....your case, or open bench or whatever. Take efficiency ratings with a grain of salt. If you can take a look at jonnyGURU, HardwareSecrets, HardOCP, and look at their PSU reviews and especially look at efficiency results in the hotbox, because efficiency ratings at 25°C really don't tell the whole story.....guide line only, not a rule.

Hope that helps.
 

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I was actually looking for sources of info about what differentiates good psu from bad ones. A lot of the time, I see people recommend Corsair anything as "the best option" without really being able to understand why. Thanks to all of you guys who try to help newbs like me be informed !
 
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