I lost power once 2 weeks into incubation. The temp in the incubator was 78 degrees when I discovered it. I put the incubator on a battery pack with an inverter and brought the temp back up. I still had a good hatch. There is a thread on BYC where several others have either lost power or had power spikes and I think their hatches went ok. It takes time for the eggs to cool down so I don't think that really affected the hatch.