Ausgrid has restored power to all 23,000 homes and businesses it says were affected by blackouts across Sydney and the state's Hunter and Central Coast regions.
Outages were experienced on Wednesday in a number of suburbs including North Ryde, Wheeler Heights and Narraweena, where about 3,200 customers were left without power.
Crews worked throughout the afternoon to restore electricity to almost 4,000 homes and businesses in Punchbowl and Bankstown.
On the Central Coast, about 3,600 homes and businesses were left without power in parts of Narara, Blue Haven and Green Point, while another 1,600 homes and businesses were affected in Erina and Green Point.
The electricity provider also spent the day looking into what was behind the high number of blackouts.
"Demand is running higher than ... this time last week on the network," Ausgrid spokeswoman Zoe Allebone said earlier.
"But the network is definitely operating within capacity, so at this stage we don't believe that it's an issue to do with the load on the network.
"Obviously on such a hot day we understand it's very inconvenient for our customers to have the air-con go off, or the fan go off, and we do apologise for that inconvenience."
Ausgrid has not yet confirmed the cause of the blackouts in each of the areas, but it has said there were a number of different factors at play.
"Today's interruptions were caused by a range of factors, including damage to powerlines at Punchbowl and Caringbah," the company's statement said.ABC