The 550w is a server unit with 24 pin ATX connector and a higher 12v rail (36a), while the 530w is more intended for desktop systems. I would suggest using the 530w myself, but the 550w will do if your board uses the 12v for CPU power (the 5v and 3.3v rails are a little weaker on this one to allow for the 36a @ 12v).
If getting the 550w, I would contact the vendor and be sure it comes with the necessary adaptors - 24 to 20 pin ATX and 8 pin to 4 pin ATX12v.