I'm planning on making this build with a few replacements (5770 instead of a GTX 460, and a Caviar Black hard drive). My question is whether or not I can use my old power supply or buy a new one. The old supply is a Thermaltake Purpower 2.0 500w with 14A and 15A on the +12V rails. I've read a few comments that say the Purepower's are crap. What do you all think?