The remaining generators might help keep the lights on for hospitals or police stations if the island gets hit again during the coming hurricane season, which begins June 1.
Hurricane Maria devastated Puerto Rico last September, leaving 1.5 million homes and businesses in the dark. Both the island's power utility and the Trump Administration's Federal Emergency Management Agency were criticized for a slow response.
Most power has been restored by the U.S. Army Corps of Engineers but the electricity grid remains unreliable, and suffered an island-wide blackout last month.
"The whole world is very nervous about hurricane time," said Rosalina Abreu Gonzalez, who lives near Mariana, on the eastern side of the island, where power has still not been restored. "There is a real concern - the government hasn't provided an energy system that is more secure."
The Army Corps, a unit of the U.S. armed forces, has said its task is largely complete now that most people have power. About 22,000 customers are still without electricity, most in remote areas, according to the new head of the island's power utility, the Puerto Rico Electric Power Authority.
"Our mission wasn't to build a modern resilient system," Charles Alexander, Director of Contingency Operations and Homeland Security Headquarters at the Army Corps, said at a Senate hearing last week.
On April 29, Governor Ricardo Rossello asked U.S. officials to leave behind 850 generators at critical facilities, along with three larger generators used to keep the grid stable. FEMA agreed to leave the mega-generators and generators for 700 critical facilities. Mega-generators supply 75 megawatts of power, enough to power 75,000 homes.