The reason why some people recommend PSUs with way more capacity than is actually needed is because they just don't know what they're talking about (and so they shouldn't even be trying to help).
Here's one thing that many people don't know: the power supply requirements that AMD and NVIDIA state are in regards to PSUs with a "peak" rating. So let's look at the power supply requirement for the GTX 470:
So this means that they are recommending a 550W peak-rated
power supply to power a system that has a single GTX 470 in it
(it's for the entire system, not just the graphics card). In addition, they're likely also taking into account the chances that the person who buys a GTX 470 has the latest system (that is, whatever is the latest at the time the graphics card was released) instead of what I have (see my sig rig).
Therefore, we can summarize it by saying that power supply requirements for graphics cards are always bloated, especially for overclockers. The reason why is because almost every experienced overclocker (or everyone who's experienced in building computers) is using a quality power supply. Most quality power supplies (i.e. recommendable
power supplies) have a "continuous" rating. For example: my power supply has a 650W continuous rating. One giveaway is that the +12V's wattage capacity is very close to the wattage rating of the entire power supply (624W, 26W shy of the 650W rating).
If you're wondering why I am using the HX650 to power my little system, it's because I originally wanted the HX450 (I like the look of the HX series), but the cost after international shipping made it more expensive than the HX650 at that time.
Another reason why people recommend an overkill power supply is because they don't know that having overkill negatively effects the PSU's efficiency:
On PSU Efficiency
PSU "50% Load" Myth
Others simply think it's much wiser to have extreme overkill because that means you never, ever, ever, ever, ever have to worry when you upgrade. However, these people are failing to take these things into consideration:
- The cost of an overkill PSU
- The lower efficiency due to the extremely tiny power draw on the PSU
- The chances of having poor PSU performance due to having too small of a power draw on the PSU - even with a top-quality unit.
- The chances of others seeing what you have and thinking "Well, if that's what they're using to power their system, then that must be what is needed. So, that's what I'll get". I mean, some people prefer to just look at what everyone else has instead of "bothering" us with a new thread. Heh.
Finally, another reason is because they don't know how to use online power supply calculators correctly.Edited by TwoCables - 3/25/11 at 4:54pm