Considering those 680's are OC'ed they will be consuming more power, I probably wouldn't run anything less than a 850watt PSU with some good amps on the 12v rail. The 770 consumes more power as a individual card versus the 680 and with it being a OC'ed AMP video card, I wouldn't consider anything less than a 850watt but perferably 1000watt with those in SLI. Some people will tell you that 750watt is enough, but you need to take into consideration the factory overclock on the cards and the other components of your PC. Plus you need to factor in %10-20 more for capacitor degregation over time. My suggestion, look at something like the Corsair HX850 if your going to run the 680's in SLI or the EVGA Supernova G2 1000watt if your going...