I have a coffee maker and microwave oven that run off AC and both have clocks. After a momentary power outage the coffee maker will display the correct time * but the microwave will show a flashing 00:00.
*or at least the time the power went out. If the time advanced from 1:32 to 1:33 during that momentary power outage I don’t know if it’ll be a couple seconds slow or not when the power returns.