The monkey fell on a transformer at the Gitaru hydroelectric power station on Tuesday, electricity provider KenGen said in a statement.
The transformer then tripped, resulting in the loss of 180 megawatts of power and triggering a blackout across Kenya.
Power was restored almost four hours later and the monkey survived its adventure, KenGen said.
It has now been taken in by the Kenya Wildlife Service.
"KenGen power installations are secured by electric fencing which keeps away marauding wild animals," the statement said.
"We regret this isolated incident and the company is looking at ways of further enhancing security at all our power plants."
The Business Daily Africa website reported that businesses bore the brunt of Tuesday's blackout.
Many had installed generators as a result of previous blackouts, it said.
A single monkey caused a nationwide blackout in Kenya after falling on to a crucial piece of equipment.