NVidia GeForce 7950GT vs HD 3870

No i wouldn't try and run a 3870 on that PSU, depending on the rest of the system you could either go for a 4670 or a 5670.
Which to me would very much depend on your system. If its casual gaming you want then the 4670 is fine and isn't that far behind the 5670. if you want the best you can get then its the 5670.
Budget wise i don't know what the difference is but as i said in benchmarks its close.
At the end of teh day its going to depend on what you want out of it, there are too many things to go into with out knowing so if you need more help let us know the system specs and what you want out of the card and we can advise a bit better.
http://www.techpowerup.com/reviews/HIS/Radeon_HD_5670_IceQ/8.html

mactronix
 
I think there may be a very important part of information you're not providing and would likely help people give you better recommendations..... This is for AGP isn't it?

Anywhoo, either way, it is a very noticeable upgrade (as long as you have a good CPU), but I agree with Mac, you may need a new PSU. As good as Fortron PSUs are, that's alot of draw for a 400W aging PSU, you could try it, but I'd expect problems. At which point if you need a new PSU might it make sense to simply get a new mobo and PCIe HD5670 which would outperform both and likely still work on that old PSU.

A little more information about the system and pricing would be helpful. :hello:

 
Fortron PSUs are pretty good. It should be able to handle your system with a 3870, if you don't have alot of drives and a heavily overclocked PC anyway :D. The 3870 is a pretty good upgrade over the 7950GT. If it's worth it just depends on how much you're going to pay for it. A 4670 performs just a little slower while being generally cheaper.

What's your budget?