Anything that causes a fluctuation in the power good signal from the power supply will cause a reboot. Generally a flicker in the incoming power, or a brownout.
I would suggest the UPS like mrregan , but I would go further and suggest something like the APC650 or higher with the monitoring software for SCO for auto shutdown when the UPS is about to close up. Ed Fair
Any advice I give is my best judgement based on my interpretation of the facts you supply. Help increase my knowledge by providing some feedback, good or bad, on any advice I have given.