With only 36 amps on two 12 volt rails and 430 to 460 watts of power

With only 36 amps on two 12 volt rails and 430 to 460 watts what card could I use in my son's much older, original pc that has a socket 775 e5200 and would be better than his current 9800 GT?  He games in 1080p when he pc games.

260x is a good place to start. Not too costly, and it is balanced with the rest of the system. Reasonable medium setting 1080p card. For a little more performance, you might consider the R7 265, or alternately, the 750ti. Those cards will handle most games on a mixture of medium-high settings.

It would be advisable to overclock the E5200.

I have overclocked the cpu to 3.0 GHz but it won't go any higher without more voltage and other tweaks. I am looking at getting a 1 GHz improvement from it. I had gotten two other pcs supposedly overclocked stable (24 hour testing) but have been getting blue screens so I kind of put working on that pc on hold. As for the video card recommendation info. thanks.