Best case you just get some freezing and choppy game play, worst case you get BSOD every time you load a game. It also depends on the brand, if its a cheap PSU, its likely that the 430 watts it does have are directed towards the 3 and 5 v rails and the 12v is at like 12 or 15 amp. I had a cheap PSU that was 480watts, but it only has 12 amps on the 12 volt side.