Nearly 1,000 homes in Haywards Heath lost power due to an underground cable fault on Tuesday night.
Power was interrupted to 973 customers in the Isaacs Lane area at about 9.20pm.
The majority of supplies were returned to normal by about 10.30pm.
The remaining 160 customers had their supplies restored by 2.30am on Wednesday.
A UK Power Network spokesman said engineers worked hard to get power back to customers.
He said: “We realise how difficult it is to be without electricity and apologise for any inconvenience caused.”