Yeah it kills the server. The one on battery doesn’t sustain anything. The UPS is not giving any backup power for black/brown outs for that particular server regardless now.

Is this really just PSU? Or it’s tied into the MB somehow?

Both PSU do the same though. It’s not specifically one of them. Whichever ups I put on battery, the PSU will act like it’s not getting power.

Simulated sine wave. The weird thing is my 2 other supermicro servers on those UPS don’t have that issue, it’s just this one.

The alarm is normal, if you unplug 1 PSU it warns that something is wrong. But it shouldn’t do that on UPS battery. Server keeps running because other PSU supplies power to server.