You say at regular intervals. Can this interval be timed to the second, what about the time of day, is it doing at the same times. Check the configuration of the monitoring software on the UPS. Other hardware in/attached to the server. Do you have Dell’s Server Administrator installed. Is there anything in the logs there. Check the settings in Server Administrator, there are settings that can shut down the server on temp/voltage/current faults. Run diagnostics usign Server Administrator. I would focus on that UPS monitoring software on the server if it is installed.