I'm thinking mobo, too. As unlikely as it is; however, I would try testing each PSU by doing the paper clip test. I don't usually recommend this test, as the results are often false positives, but let's rule out PSU. Grab a paper clip. Open it up so that you can jump the green wire and the black wire next to the green wire. Do this to all PSUs. If all of them turn on, then the likely culprit is the mobo. If none of the PSUs turn on, try changing the power cord that goes from wall to the PSU.
I tried the paper clip test on both PSU and both power up fine. I RMA'd the mobo, hopefully that fixes the problem.