Weather-related outages have been particularly stubborn in Oregon, where some customers have been without power for almost a week.
The worst U.S. outages by far have been in Texas, where 3 million homes and businesses remained without power as of midday Wednesday.
AdThe president of the Texas power grid manager, the Electric Reliability Council of Texas, said he hoped many customers would see at least partial service restored by later Wednesday or Thursday.
At the peak of the storm, more than 350,000 customers in the Portland area were in the dark.
In Oregon, authorities confirmed Tuesday that four people died in the Portland area of carbon monoxide poisoning.