Some outlets are reporting a fire in the southwest of France is to blame, but French electricity providers have denied the claim. Portugal’s National Cybersecurity Center also said there was no evidence of a cyberattack being behind the power outages, state news agency LUSA reported.
While the exact cause remains unclear, governments have convened emergency meetings and electricity providers are working to restore power as soon as possible.
I do see other news articles on other sites speculating as to cause, including some about hacking, but that doesn't seem to be beyond guesswork. I'd think that if there were any firm information out, that CNN would have it.