That's one of the PSUs I bought to try. So, good!

I can simulate the 2 min interval reboot, which seems to be part of the blade's firmware if it doesn't sense a connection to any pool it reboots after roughly 2 minutes assuming it's "dead/sick."
Where it's such a regular interval I have a hard time believing it's lack of power, but it's certainly possible. When I checked the blade's power usage with the kill-o-watt I saw about 650W at full load. I will have to throw it back on and keep an eye on what it does when the unit reboots. I haven't had a chance to catch it in the act yet to see if the PSU has any change in the LED or something like that.
There has to be a reasonable explanation for this, even if it's a hardware problem.