if so, would it be by a great deal? I have a gtx 295, amd phenom ii 965 quad core, but only a 500watt power supply. from what i've heard, 500watt probably wouldn't be enough to power everything adequately, so I reduced my gpu's core, shader and memory clock to minimum. I currently don't have the cash to buy a decent power supply, so I don't want my current one dying on me any time soon.
Since so many power supplies are inaccurately labeled for power output, it would be helpful to know the brand and model number of your existing PSU.
There are PSU labeled "500 watts" that will blow up when you draw 250w, and some that will do 550w without breaking a sweat. Thats a pretty big spread.