for a 5750 they recommend 450w, but if you have a few hard drives, a decent motherboard and processor and case fans, and ram, this'll all add to your heat, which then adds to the wattage needed to keep everything cool. And then you've got your USB devices, which all run off the same PSU. I have a 4870 and they recommend a 550w, which I had and it blew. You're safer going for at least 100 - 150 watts more than you need to make sure that whatever you're running and other peripherals wont take too much juice at the same time the GPU kicks into overdrive. Trust me, if you go for a 500w PSU you'll regret not going to 600w in a few months or even next time you upgrade.