You should understand that in every line of graphics cards from both major brands, there are 3 types of GPU's. There are the cheap modles that supposrt the basic new technology (such as the latest vertex shader and etc) but are basically just good enough to surf the web. The 7300 is one of these.
Then there are the made for gaming chips such as the 7950 ultra, or the 8800gtx, the 6800 ultra, the old 5950 I used to own and even the geforce 4 ti4400 I had before that. The cards (when new) were designed to be the top of the line cards.
The third type are those which can be consittered budget gaming cards, they have the power to do more than surf the web but they are not hardcore either - for example ati had x600le, they were better than the x300 but not as good as the x850xt.
How does that relate? Well, the bottom cheap class (being that it doesnt render hardcore anything) doesnt need alot of power and can get away with using a little power. However, you can actually buy an older card but one which was meant for gaming such as the 6800ultra and they reccomended PSU is 480 watts. The point bein that, it doesnt necesarel depend as much on which serries you get as it does how powerfull the card is. Posting the exact card you are looking at will help greatly.
For more information on power supplies as well as a link to a powersupply calculator, look for my thread in tech talk.