They added that Pepco had "no objection" to removing periods of major outages from their billing calculations in Maryland.
Pepco officials noted that because of extreme temperatures in 2010, the system resulted in a $3.3 million credit for Maryland customers. The adjustment applies only to the distribution portion of customers' electric bill, the roughly 25 percent that pays for delivering electricity to a home or business. Pepco no longer generates electricity.
For a typical Maryland residential customer in 2010, Pepco said, the monthly credits averaged $1.88 and monthly additional charges averaged $1.59.
Some customers were angered over the possibility of paying for the outages.
"That's just mind-boggling," said Michael Weiner of Gaithersburg, whose family went without power for five days last week. He pointed out that no one has sought to reimburse him and his neighbors for food that spoiled during the outages.
The Maryland Office of People's Counsel, which represents consumer interests, asked regulators to reconsider the arrangement last month, saying Pepco should not be rewarded with additional revenue if the blackouts were extended by "deficient service." Paula M. Carmody, who directs the office, said this week that she welcomed the commission's action and that the billing system needs to be modified or scrapped.
A Washington Post investigation published in December found that Pepco's day-to-day reliability began declining five years ago and that Pepco ranks at or near the bottom in national surveys of reliability. The average Pepco customer experienced 70 percent more outages than customers of other utilities in major metropolitan areas.
Berliner described money Pepco had collected after major outages as "ill-gotten gains."
"Every dollar should be returned to consumers as a small step toward making it right," Berliner said. "You take the dollars Pepco has earned in all the outages since 2007, I would be shocked if it wasn't millions of dollars. They got dollars they never should have gotten."
Staff writers Katherine Shaver and Mary Pat Flaherty contributed to this report.