It should be compatible with the motherboard.
The 620w Seasonic should be fine, max power for the GPU is less than 225w. It only has one 8 pin connector which can carry 150w plus the 75w of the PCI-E itself. I have no idea where these knuckleheads were getting 500w for the GPU, that number is the recommended minimum power supply for an entire system that includes this GPU.
InternalSurge, no way would I run this on a CX500, especially since you list an FX processor in your sig. An FX processor and this GPU alone are around 315-325w. On a PSU that is of lower quality and only puts out 356w when new is asking for at least a fried PSU.