I have had the same question for my sc5520 mainboard.
I found out that you will need at least a 570Watt PSU.
What I have done is I bought a original Intel server case. SC5600Base.
This one comes with a 670W psu and is compatible with tha mainboard you describe. So 2 CPU power connectors are availble. I 'll think if you are looking for a power supply with 2 cpu power connectors that it wil cost you a lot of money. Also be awera that the PSU must be stable and be able to provide the amount of current at all time at all line's so check the specs. and compare them with the PSU of teh Intel power supplies.