It's not impossible that the power outage - or more specifically, how the power came back - could have created a brief power surge on the AC line that (somehow) transferred to the USB-to-Ethernet adapter and fried it. The "somehow" is the tricky part. Neither USB nor Ethernet are normally associated with the AC line, so it's not obvious from what you wrote, how that would happen.
However a common cause of adapters frying is ESD - electrostatic discharge - typically from a person's body. The old thing of shuffling across a carpet and touching a doorknob or light switch and drawing a spark. It's winter, humidity can get very low, and dry conditions make ESD much more likely.
So I would place my bet on ESD and a coincidence with the outage. But that's just a guess.
BTW, ESD can kill electronics at a surprisingly low level — too small for you to feel or hear or see. It doesn’t have to be a visible or “feel-able” discharge to damage electronics.
I'm a firm believer in the weirdest things are more and more showing up in our lives as we approach His Second coming, revival in America, or Satan is REALLY freaked at what the miracle of President Trump has in store for him.