The outage, which affected approximately 575 customers in the Potrero Hill neighborhood, was first reported around 8:30 a.m., PG&E spokesman Joe Molica said.
One of the workers who responded to the neighborhood was injured when a transformer failed during an initial investigation, Molica said.
The male worker suffered minor burns and was taken to a hospital, Molica said. The man is expected to recover.
PG&E was working to replace the transformer and plans to conduct a thorough investigation into the incident, Molica said.
Power had been restored to all but a few dozen customers by 1 p.m. Sunday.