Originally Posted by Ninja Prime
I'll never buy anything but Corsair power supplies again, best PS ever. Corsair power supplies are rated on actual power, the 620w, which I have, it equal to a 750w 80% efficent PS from anyone else. 620w should be plenty for any single card.
I think you're misunderstanding the efficiency rating. It has nothing to do with power output, so much as power input.
For instance, my SeaSonic S12 500 can output 500W (if you max out every rail). It's also rated as 80+ efficient, so for this argument, we'll use 80% as it's efficiency.
Since energy is lost in the form of heat, the PSU has to draw more power from the wall than your PC actually needs. So, if your PC needs 200W, and the PSU is 80% efficient, the actual power draw from the wall would be 250W. No PSU is 100% efficient, and most high quality PSUs, including SeaSonic, PC P&C, and several others, can output their rated power.