Blackouts are common in Kenya, partly because of an ageing energy network and insufficient generation capacity.
By 1000 GMT supply had been restored to all major regions including the capital Nairobi, West Kenya, North Rift, South Nyanza and the Coast area, the company's spokesman told Reuters.
"We experienced a technical challenge that led to tripping of our main supply line ... consequently leading to a power outage in most parts of the country," Kenya Power said in a statement early on Saturday.
Kevin Sang, Kenya Power's chief communication's officer, told Reuters supply was knocked out at 5:34 a.m. local time (0234 GMT) on Saturday when a fault occurred on a transmission line that runs from Olkaria in Kenya's Great Rift Valley region to Nairobi.
Blackouts are common in Kenya, partly because of an ageing energy network and insufficient generation capacity. Many businesses in Nairobi and other big towns operate back-up generators.
"There could be pockets here and there ... which are still off supply but most of the areas are back on supply," Sang said.
Motorists drive into a roundabout linking Mombasa road and Uhuru Highway towards the city centre in Kenya's capital Nairobi