I just read news of the power outage in Spain and Portugal. Apparently it started with the interconnect between the two countries, and caused rolling outages in both. I presume that is due to remaining generators being overloaded.

It's a common problem in an interconnected grid, since none of those systems are capable of carrying the full load they're connected to.

There was a partial outage in Texas in 2021, and they intentionally didn't connect to the grid in other states. It was a close thing.

"According to the Electric Reliability Council of Texas (ERCOT), the Texas power grid was four minutes and 37 seconds away from complete failure when partial grid shutdowns were implemented."
https://en.wikipedia.org/wiki/2021_Te...

If they had completely lost power, they would have a big problem getting it back up. It's called a black start.

Why am I talking about that? Because my novel is post-apocalyptic: a brief nuclear exchange. Although many cities were untouched by the bombs, enough of the power grid was knocked out that most of the rest of the world couldn't maintain the grid and so it all went down. It reduced nearly the whole world to frontier-level.

Part of the novel's plot is efforts to restore power in the USA.