I wonder what it really comes down to for you to decide.
You can find web sites with benchmarks or just consider that it's common to pop in a new supply. It doesn't have to be expensive either. At the office we use those 25 buck 600 to 680 Watt PSUs since they are cheap and we know they couldn't possibly be 680 Watts but they are more than enough for our machines.
I'm having trouble choosing between the ATI Radeon X800 XL (256MB, PCI) and the Radeon x1600 pro PCI express. Heres the situation, I can purchase the the x800 XL and install it right away or I can get the x1600 but would have to buy a more powerful power supply unit (which I would be willing to do, if it gets me better graphics). Both video cards cost roughly the same amount. The x800xl has gotten nothing but good reviews, i'm unsure about it being able to play most current and future. I need a video that card mainly to play video games, any suggestion of which is the better? Thanks