I bought A pre-build PC, (Asus CM6870) That came with a Nvidia Geforce GT 620, and a PSU of 300-350w PSU, and I had no choice to upgrade my GPU if I wanted to play games higher then the lowest settings possible in games, so what card would match a new PSU, that would be reasonable? I am thinking of something around a 650-750 or 700W, and if I am not using all of the power necessary for all my parts, where does the extra watts go? Do they just sit around? Thanks for the answers!
At 650 to 750 watts, you can run pretty much any single graphics card you want easily.
A PSU draws only the power it needs for the tasks the computer is doing. Light surfing or watching vids, less power is drawn from the wall from the psu. On the other hand playing modern games or video editing will push your system and draw more power.