The FBI’s Seattle field office declined to comment on the incidents nor confirm reports that the agency has sent bulletins to local law enforcement agencies and utility companies warning of attacks, but said the agency “routinely shares information with our law enforcement partners to assist in protecting the communities they serve.”

I think it could be the US government doing tests (without the political blowback of deliberately shutting off people's power). Because there's been plenty of media about how rickety our electrical system is. They want to see how people respond to abrupt power outages and stuff.