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
Underground power lines are weirdly vulnerable to lightning strikes.
I lived through two >24hr power outages at my previous place that had buried power lines into the subdivision. Both due to lightning strikes on trees that happened to be close to the buried lines. The lightning then fed into the line, and you could literally see black scorch marks on the lawn that followed the wiring until it eventually dissipated.
This required digging up 30-40ft of melted wiring each time and re-running it. These appeared to be direct-burial cables fwiw.
Talking to the utility guys, it was pretty common for this to be the failure mode. I found it pretty interesting and somewhat ironic.
My neighborhood has underground power lines and we lose power every time there is a hurricane/tropical storm or even a major thunderstorm.