MSI is a good brand too look for, gives 3 year warranty on most cards, enhances gpu speed on some cards, will provide help when needed, comes with alot of tools on Driver cd, and so on.
Evga is also good, Warrantys and so on.
MSI, Nvidia, and Evga is some of the most powerful GPU card producers, and Warranty givers.
I've actually ran a 500w video card on a 400w power supply, never had any problems..
Also, when you look for cards, you must look for certain features/requirements. Such as, PCI, PCI-E(Express), if your motherboard doesn't have these slots, or your power supply, and your vid card requires it, it won't work. Some video cards require a (24 + 4) Pin Mainboard Connecter to get full power, Again if your board, PSU, only has (24) pin mainboard connector, you won't get full power. Some video cards use (4) pin mainboard connector, some (4 + 2) pin mainboard connectors..
High Pixel shader, 3.0 to 4.0 is very nice when playing high-end games. Open GL helps on some High-End games that use it.
So as you can see, a whole lot of factors you need to look for. Would be more helpful if you posted your PSU.