The outage was reported at about 7:15 a.m. and affected customers in South San Francisco, Brisbane and San Bruno, PG&E spokesman Joe Molica said.
Shortly before 8:10 a.m., power was restored to about 15,000 of the customers, and the remaining customers had their power restored by 9:55 a.m., Molica said.
The cause of the outage remains under investigation, but early indications are that it was caused by a problem with a transmission line connecting to a substation in the area, according to Molica.