30 amps, you would be fine with a 9800gt. If your worried, a 9600gt uses a little less power, and is a bit cheaper. And the 8800gs/9600GSO is also a decent card for the price.
Another thought, If your worried about your power supply, you can upgrade it for cheap. There are many QUALITY power supplies for under $40, that might make you sleep a bit better at night. lol
Just a suggestion.
What's your budget?.