My parents have underground power lines, and they've lost power multiple times, from vulnerabilities in the infrastructure. The transformers are still above ground, in big green boxes, and occasionally someone will drive into one and knock out power. The substation is also above ground, and once they lost power because a mylar balloon landed in the substation and shorted some lines.

They've also lost power from rolling blackouts due to not having enough power plants, but that's a California thing, at least compared to first-world countries. In a similar vein, a substation in the city my dad grew up in was once taken out by a sniper: https://en.wikipedia.org/wiki/Metcalf_sniper_attack