Had a brief power failure the other day. How brief? A monitoring device I have showed the voltage dropped to 31V for 28.5 cycles. That means it dropped to 31V for 475ms, 1000ms in a second so that was less than a 1/2 second.
My PC rebooted and I had to reset a few clocks and my router is on a battery backup. Can’t say if the the MC was in sleep mode but when I thought to look at it the LED was blue.