Additional power was being shipped from Mexico, said Sempra Utilities (SRE) Chief Operating Officer Michael Niggli. About 19,500 customers were without power Wednesday either because of downed lines or to ensure the safety of firefighters, officials said.
Towns scattered throughout the county remained on the edge of disaster, including the apple-picking region around Julian, where dozens of homes burned in 2003. To the northeast, in the San Bernardino County mountain resort of Lake Arrowhead, fire officials said 6,000 homes remained in the path of two wildfires that had destroyed more than 300 homes.
Both fires remained out of control, but were being bombarded by aerial tankers and helicopters that dumped more than 30 loads of water.
Losses total at least $1 billion in San Diego County alone, and include a third of the state's avocado crop. The losses are half as high as those in Southern California's 2003 fires, but are certain to rise.
The more hopeful news on the fire lines came a day after residents in some hard-hit San Diego County neighborhoods were allowed back to their streets, many lined with the wreckage of melted cars.
So far, at least 15 fires have destroyed about 1,500 homes since they began late Saturday. The burn area of nearly 460,000 acres (186,160 hectares) stretches in a broad arc from Ventura County north of Los Angeles east to the San Bernardino National Forest and south to the U.S.-Mexico border.
In the middle of that arc, the Santiago Fire in Orange County had burned nearly 20,000 acres (8,094 hectares) and destroyed nine homes. Only 50 percent contained, it is a suspected arson fire.
"Whoever has started this has started it at different points that indicated that they wanted it to grow rapidly," Kris Concepion, an Orange County fire battalion chief, told CNN Thursday morning.
Agents from the FBI and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives were sent to help investigate. Authorities said a smaller, more recent fire in Riverside County also is linked to arson.
Despite the widespread destruction, the fires have directly claimed just one life, 52-year-old Thomas Varshock of Tecate. The San Diego medical examiner's office listed five other deaths as connected to the blazes because all who died were evacuees.
The number of victims could rise as authorities return to neighborhoods where homes burned. In 2003, 22 people lost their lives in a series of fires that lasted nearly two weeks.
-- Wires services contributed to this report.