we have been seeing this on and off for about a year now. we too thought it was power issues. we have since deployed UPS's that show no power issues. other extreme switches hooked up to the same UPS did not reboot at the same time. we have just updated to the newer software. 16.1.3.6 patch1-11, but are still having the issue. do you have a gtac ticket open? I am opening one now for a switch that just had a reboot.