Video Card problems. HELP!!?

http://www.compusa.com/products/product_info.asp?pfp=srch1&Ntt=a6230n&N=0&Dx=mode+matchall&Nty=1&D=a6230n&Ntk=All&product_code=347464#ts



I own this computer, and the video card installed (nvidia geforce 6150 SE) in it stinks compared to the system specs. I was hoping to get a video card, but I don't think the computer has enough PSU to support a good video card.



...question is: Which video card can I get with my standard PSU?



*computer has 300 watts PSU|||It would be cheaper for you to just buy a 400 Watt PSU.