Electricity was restored around 10pm on Thursday night to around 12,000 homes and businesses in north Wicklow and south Dublin which had suffered power cuts for several hours.
A spokesperson for ESB Networks said the worst affected areas were Bray, Greystones, Delgany and Shankill.
The outage was traced to a fault at an ESB substation in the Fasaaroe area of Bray, while there was also a related problem with a high-voltage cable in the same area.
The spokesperson said emergency crews had worked at repairing the fault which first emerged at around 7pm on Thursday.
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ESB Networks has apologised to all customers affected by the outage.