This is a weird thing I have happening on one of my servers, these have been running nearly 7-8 years but I recently swapped a new MB/CPU etc in a server. IT’s SC836 dual redundant PSU.
So both PSU are plugged in it’s own UPS. When I pull the plug from the wall, the PSU that’s on battery will go yellow and scream loud alarm. Mind you other servers are connected to this UPS getting battery powered AC. Only this server does this. I tried it with both PSU and both do the same thing. Is something wrong with the chassis PDU/PMBUS or something else like MB/ram/CPU?
Assuming this isn’t user error, where you have your Server plugged into outlets that are only surge protected and not battery powered, you have it backwards. Your server, or more specifically the power supplies, power controller, and the BMC (if you have one), aren’t DRAWING any power from your UPS because they don’t consider it clean enough to use. The UPS doesn’t “give” anything.
Check to make sure you’re using ports that are powered under battery and if so your options are to get a new UPS that generates a pure sine wave, get a new server that doesn’t care, or just plug it straight into the wall and know that it will shut down during a power outage.