I have no idea what the power supply is. I've never opened my tower, and I'm pretty sure I have to do that to see the power supply. But since my video card has been being weird (I get these boxes that appear on the screen and it slowly starts filling the screen, then the picture locks up. But when I press Ctrl+Alt+Del it will still bring up the menu thing for logging off and stuff. I have Vista. It used to just come back itself and tell me an error relating to "amdkmdap", but recently it's only been fixed by restarting the computer.) I don't play tons of new games (because sometimes it seems like they lag, despite having a quad core), but usually I play at 1280x720.
As for price, I'd say around 100 dollars.