In Concord, an outage that began at about 3:40 p.m. initially knocked out power to 4,700 customers, PG&E spokeswoman Jana Morris said.
As of 6:15 p.m., only 950 customers in the region bounded by Ygnacio Valley Road, Alberta Way, Lime Ridge Open Space and Clayton Road were still without service.
Some 385 customers in San Jose remained without service after power went out at about 1:15 p.m., Morris said.
In Redwood City, 846 customers lost service at about 4:50 p.m.
Even though causes of the outages were still under investigation, Morris said crews were working to restore service to customers before repairs were made.
"Sometimes with the way that our circuits are laid out, it allows us to restore power while repairs are being made," she said.
Morris said that there was no estimated time of restoration for any of the three outages.
KGO contributed to this report