Originally Posted by FabTheZen
From what I read, even the 650w would be an overkill for a single card, yes, but I can't do SLI even with a 750w, even with mid-level cards such as 2xGTX 760, is that correct? (A source I used is this: http://www.realhardtechx.com/index_archivos/Page362.htm
However, i'm planning to buy a graphics card later this year, maybe a GTX 770, not going to OC unless very later, just for longevity purposes. Right now I have a GTX 260. Would it be a waste buying the 750w? Do you have any other PSU to suggest?
The 700W recommendation is for peak-rated PSUs. The typical 700W peak-rated PSU would have a +12V capacity of 504W, which is the same as some semi-decent 550W PSUs. Check this out:
With two GTX 760s under full load, their PSU pulled 449W from the wall outlet. Their CPU was idling, so I have to add up to 150W for a well-overclocked CPU. Adding this to the 449W makes the PSU pulling 599W from the wall outlet. If we assume that the PSU is 90% efficient while pulling 599W from the wall, then that means the computer is pulling 539W from the PSU. Your gaming power draw will be lower, peaking at roughly 500W. Therefore, a good peak-rated PSU to recommend is a 700W unit, but a good quality-made PSU that can be recommended is a good 550W PSU because most of them would have a +12V capacity that's at least 540W.
A good rule of thumb is, multiply the professional PSU recommendation by .72. Then, find PSUs that have a +12V capacity that matches what you get, or that come close to it. That's what I did there and it worked out perfectly to 504W which is a common +12V capacity of semi-decent 550W PSUs.
If you want to find the amperage, then divide by 12 because it's 12V power. If all you have is the amperage and you want to find the wattage, then multiply by 12 (because it's 12V power).
Anyway, yeah if all you're going to do is have one video card and you'll maybe overclock it, then a good 750W would be a waste. I would say that a better purchase would be a good 450-550W PSU unless you know that you'll have two mid-range to two high-end video cards. Then, having a good 650W PSU should guarantee that you'll not only have enough power, but enough PCI-E connectors. You could use Molex to PCI-E adapters, but they can be butt-ugly. hehe