I have a Dell PowerEdge R710 that I inherited from my company when it was retired. I have it protected with a CyberPower UPS, but every time there is a power failure, the server reboots. I have tried two separate UPS units. The old one was a 1000VA AVR unit with simulated sine-wave output, which I now use for my desktop. I just bought a new UPS for the server which is another CyberPower 1000VA, but with Pure Sine Wave output plus AVR. This unit has the same symptoms.
With both UPS devices, the server remains on when performing a self-test of the UPS, and will run on the UPS's battery after rebooting. However, a true power failure (unplugging, turning off the breaker, or the power actually going out) causes the server to reboot and then turn back on. I have tried the highest sensitivity level of the UPS (smallest band of line voltages outside which the UPS will switch to battery). Even on the highest setting, the server reboots.
Is this an issue with the server's PSUs, or with the UPS devices? I have both PSUs connected to the battery backup side of the UPS.