Brand new (relatively) high quality 80%-efficiency with UPS. I'm confident that my PSU is generating stable 12V for the mboard. I measured the 5v power coming out of the m-board pins and going into the RPi. It's weird... first it's at 5.39V but it keeps increasing every couple seconds. In any case, 5.39V is beyond the maximum (5.25V)
What I'm finding is that the polyfuse F3 (near the micro-usb connector) gets really really hot - finger burning. Is yours like that?
What brand of PS and what brand of UPS?
rosewill rg-530, cyberpower ups
I had VERY bad luck with cyberpower. I had six, three died turning off the servers they were supposed to protect.
Not to pile on here... but aren't Rosewill PSUs pretty much 'bottom o' the barrel' too? They're Newegg's private budget label.