Originally Posted by shilka
Its far better and far less trouble just buying a bigger PSU if you want 3 video cards
Your 750 is more then for two
What worries me is this:
They calculated that the 7970 pulled 195W by itself. Multiply that by 2 in order to add 2 more 7970s, and the result is 390W. Now, their system pulled 355W while the one 7970 was under full load. Adding 390W to that makes it pull 745W from the wall outlet. This isn't taking into account the likely increase of 10-20W while idling on top of their idle wattage of 163W. So, let's just call it 175W, which is just 12W more making for a total of 757W being pulled from the wall outlet. Their CPU was idling during their power consumption test, so I have to add up to 150W to cover a heavy overclock of the 3770K. This makes the PSU pulling 907W from the wall outlet. This means that if the PSU is 90% efficient while pulling 907W from the wall outlet, then the computer is pulling 816W from the PSU. Although, the gaming power draw will be a bit lower, like in the 780s or 790s.
So for 3 x 7970s at stock for gaming, I would recommend a good 850W-950W PSU.