Alanna Gladstone, a 40-year-old film editor, had landed in Portugal’s capital, Lisbon, on a flight from New York hours before the outage. She checked into her Airbnb and took a nap; by the time she woke up, the technology that the country takes for granted had gone dark.

Electricity had been restored to most of Spain and Portugal early on Tuesday after huge nationwide blackouts, although authorities were still trying to find out what caused the sudden outage.