Originally Posted by TwoCables
That's 668W from the wall. If I assume 85% efficiency, then that would mean the system pulled about 568W from the power supply. If I factor in about 150W for everything else in the system, then that would be close to 720W being pulled from the PSU under the most extreme loads.
So an extremely high quality 650W might be fine (I personally wouldn't try it), but a high quality 750W is the best choice to power a system with two GTX 480s in it while a quality 850W unit is even better.
For example, knoxy_14 is correct: the SeaSonic X-750 would be fine.
First TwoCables let me say I appreciate all the info you provide both in this thread and all throughout the forum. I was wondering what you think about me being able to add another 580 Lightning safely on my x750. I kinda figured it would be okay because of how my CPU is such a power miser, but just curious as to your opinion on the matter. My relevant info is CPU will be at a maximum volt of 1.34v, two 580 Lightnings at 1.15v, two HDDs and about 6 fans, and I would be folding 24/7
on all three. I have searched and seen people chime in (yourself included) but most of the time they just recommend an 850w because the person will be buying new anyway but since I already have it what do you think? This question is mostly driven by curiosity at this point because I would have to find a great deal on another Lightning to get it. I would still like to know, though because you never know how cheap the 580 Lightning could get once Kepler hits, and if I knew I needed an 850w then I could just keep my eye out for a deal between now and then. Thanks for your opinion/advice it will be much appreciated.