Question: When it did come back on, did the temps spike before stabilizing? My incubator is so well insulated that the heat continues to rise after it reaches the temp it's set to before coming back down and stabilizing (which is why it runs for a few days prior to eggs going in). I would think I'd have a problem if the power went off for an extended period.
if temps drop a lot yes they will spike. To avoid this you set t-stat low. and up the temp 1oF at a time till your back up to optimal temps so theres no spike.