Thanks! No, it's definitely not a power issue, I had it hooked up to a AX1200 and a AX1200i. I'll test that out this weekend.
Note that ATX PSUs are supposed to have separate "rails", each with over current protection. Thus a larger PSU has more "rails" (PCI-E) connectors but each has separate over current protection.
Adding another scenario:
a) The relay closes
b) The PSU over current protection drops the voltage.
c) he Cube sees the voltage drop and opens the relay.
d) The PSU no longer has an over current condition, restores the voltage.
e) The Cube sees sufficient voltage, closes the relay
This repeats and the relay buzzes.