Power was being restored to Hawaii's most-populous island of Oahu on Saturday after a blackout left the entire island without power on Friday.
Residents said the blackout was the largest since an earthquake interrupted power in October 2006. It began at 6.30pm.
An electricity company spokesman said he had no confirmation of what caused the blackout.
Earlier a civil defense official said it was possible a lightning strike on a transformer was responsible.
President-elect Barack Obama arrived for a 12-day vacation with his family on 20 December. An aide says they were without electricity for 12 hours until power was restored at the house at 6am on Saturday.