The power went out for more than 3,300 TECO customers in the Valrico and Riverview areas late Thursday afternoon.
About half of those customers in the Bell Shoals area had their power restored by 6 p.m., said TECO spokeswoman Cherie Jacobs, and the rest were expected to regain power soon.
A look at the energy company's real-time outage map at 6:30 p.m. showed 268 homes in the area still without power.
A substation fire was the likely cause, Jacobs said.
Earlier Thursday, another 1,400 customers in the Providence Road area in Brandon were without power. The cause was a bad underground cable, according to Jacobs.