I am currently using a NVIDIA 6150SEn force 430 to play WOW, Star Trek Online (great game!). I want to upgrade my graphics card. But my power supply is only 300W.
Will I even notice the difference on the top speed 300W cards? I dont have the money to replace the power supply right now. Should I wait until I do?
The best GPU you can possibly get for that PSU would be a Radeon 7750.
It'll do well, you can get very playable framerates on low-medium settings, depending if the CPU is fine as well of course.
Anything other than a 7750 will need a stronger PSU, but a 7750 should do fine depending on what games you'd like to play. I doubt you'll get away with some of the newest games.