Please look on ebay for psus, there are incredibly cheap $5-$50 hp server psu's around 600w. that would work great for these boards. Why in the world go for standard computer psus..
http://www.ebay.com/itm/HP-Proliant-ML570-G2-Server-Power-Supply-600W-ESP117-DPS-600CB-/170761556966
or the dps-600
http://www.ebay.com/itm/HP-Hewlett-Packard-DPS-600PB-B-Power-Supply-575W-Used-Condition-/390698876500?pt=US_Server_Power_Supplies&hash=item5af777be54
dirt cheap!
The issue is often that the quality of the power provided is much lower. There is so much variation between different PSUs in terms of electrical characteristics. Having said that, with HP server PSUs, one should be ok (in theory at least) as they should be better than the consumer-grade junk that you normally find for cheap.
scotjam