Terminal B at Houston's Bush Intercontinental Airport opened early Monday morning after the lights went out Sunday afternoon.
According to a spokesperson with the Houston Fire Department, a transformer vault started smoking after oil on the floor started heating up.
She said the issue caused the lights to go out and later forced the evacuation.
Passengers whose flights were canceled were given hotel vouchers.
Most of the flights impacted Sunday were United Express, which conducts regional flights for United Airlines.
Crews put a new transformer in place overnight and began addressing the power issues that closed the terminal late Sunday night.
By 1:15 a.m. the airport reported all operations normal at Terminal B including looping train service.