So I recently got a 2900XT and I'm wondering whether or not my power supply can handle it.
It's a 400W Seasonic PSU with a total combined ampere of 34. It'll also be power a Amd Sempron, 512MB DDR Ram X2, 5400RPM HDD, Case Fan.
shovenose is right. The 2900s have very demanding power needs and going with a lesser solution will definitely result in a future failure. They also ran very hot, so you need to make sure you have sufficient airflow before proceeding. Good luck!
It's an Antec 550W Continuous power supply that's also modular and it's +12V rails are as follow: 12V1:22A 12V2:22A 12V3:25A. It has 1 6-pin Pci-e connector and 1 6+2 Pci-e connector. Perfect for the 2900XT. Would this do good? Would I also have the ability to overclock?
The PSU should be fine, but you are on the edge of performance. OCing may be possible if you have good airflow and can keep the overall system cool. The 2900s made for great space heaters during the winter (just kidding), but they do produce a lot of heat.