HAVANA — The electricity went out Friday in Cuba, affecting the entire island’s population of 10 million after one of its main power plants failed, according to Cuba’s energy ministry.

On Friday evening, authorities announced power had been restored to about 20,000 residents of the capital, Havana, which has a population of 2 million.

Power outages have been chronic in Cuba for years and have worsened in recent months. But the situation was so critical in the past three days that the…