Yes, 20 MHz is a higher frequency than 60 Hz. While that would help for the sensor version of the design, it would not directly help for the synchronization of

Yes, 20 MHz is a higher frequency than 60 Hz. While that would help for the sensor version of the design, it would not directly help for the synchronization of the AC sources. It might help you while building a switching supply to do the AC to DC conversion, and it could help when approximating a sine wave on the DC to AC conversion. Still, all of that is quite a bit more complicated than just quickly switching in a new source when the other source drops out. (Credentials: I'm an electrical engineer and have designed and built power supplies.)