A power outage caught Unalaskans by surprise Thursday evening when most of the island went dark.According to the island’s acting public utilities director, Steve Tompkins, a failed transformer caused the outage, which occurred around 5:30 p.m. and lasted nearly five hours.“Initial indications were that a unit had tripped offline,” Tompkins said. “And it caused an overload on the other unit, which took itself offline. And it resulted in a near universal outage.”Standard Oil Hill was the only area on the island that didn’t lose power during the first outage, he said.