The outage, which PG&E officials said was the result of an underground equipment failure, initially left 9,800 customers without power.
Concord police said an underground transformer apparently exploded at about 8:34 a.m. and sparks were seen coming from a power pole near Clayton Road and Market Street.
PG&E crews were working to repair the damage and restore power to customers.
No injuries were reported as a result of the explosion, police said.
