The blackout, which began at around 11am and was resolved by 1pm, was reportedly caused by an outage at a substation.
30,000 people in the city were affected, supplier Radius Elnet confirmed via its Twitter account.
#Strømafbrydelse i København S. 30000 kunder er afbrudt. Strømmen er tilbage inden kl. 13:00.— Radius Elnet (@RadiusElnet) May 3, 2018
As well as Copenhagen S, some parts of neighbouring district Amager were also affected, according to residents who posted updates on the social media site.
Der er ikke kun Kbh S, men også her i Tårnby på Amager Landevej— Fie Veje Olsen (@FieVejeOlsen) May 3, 2018
“We are looking into the problem, which appears to have been caused by the shorting out of a substation,” Radius Elnet press spokesperson Morten Kidal said earlier on Thursday.