Power has been restored Wednesday to Amtrak's northeastern corridor after a three-hour train stoppage stranded commuters and holiday travelers. Amtrak, the government-supported U.S. passenger-rail monopoly, said power was restored after an electrical problem in northern New Jersey forced the railroad to halt trains in and out of New York City's Penn Station Wednesday morning. The power outage left commuters and holiday travelers stranded or searching for alternate transportation as train service stopped or slowed sharply in most of the northeastern United States. Amtrak did not say what caused the electrical problem, which affected rail service as far south as Washington and as far north as Boston.