i have a 400w psu, wcich states it has
+12 V at 17 amps
-12V at 1 amp
+3.3v at 30 amp
+5v at 28amp.
whats the best GPU i could run? i also have a AMD phenom tri-core 8650
and 3 gb ram.
dont need to max out the settings, just something that will cope with the newest games at a resonable set. i play on a 1600 x 900 monitor.
If upgrading your power supply is out of the question (I would do this first) I would go for the Radeon HD 6670, it is not a great card by any means, but will just barley run with your PSU. The 6670 reqires at least a 400W PSU, but I wouldn't feel extremely comfortable. If I were you I would get a new PSU, around 650W or so (650 will run most any GPU out today.) Then upgrade my GPU to something like a Radeon 6770 or 6850. You could probably do all of this for less than $200 easily.
6670 will run fine ona 400w PSU. The whole system would be lucky to draw 200w with it installed. My grandsons pc is running a 5670, which uses a little more power than the 6670, on a 230w HP power supply for what its worth.
Since you have 17a on the 12v rail we have 340W (17 times 12) ofpwoer available. While there are plenty of higher powered graphics card that would work on a 400w supply, yours only having 340w on the 12v rail limits choices esp when you factor in how old your PSU probably is.
People over-rate wattage, it's current that matters. The machine in my sig only draws 250W at 100% load, so modern tech has gotten relatively efficient energy wise, but I wouldn't go nuts and stick a GTX 680 with that 400W power supply still in place. What is your budget?