CitiPower, which supplies electricity to more than 330,000 properties in Melbourne's CBD and inner suburbs, failed to give customers notice of two separate planned interruptions in Brunswick and Carlton between January and March.
The interruptions affected a total 43 customers - one of whom was a registered life support user, the Essential Services Commission said.
The commission hit CitiPower with 11 penalty notices in the wake of the outages for allegedly breaching energy laws, which require distributors to give customers at least four day business days' written notice of a planned interruption.
Robust legislation protected customers from outages without notice, commissioner Sitesh Bhojani said.
"Protections for Victorian customers who require life support equipment are among the most critically important obligations that the commission administers," he said.
"It is unacceptable that customers relying on the supply of electricity from energy businesses are not notified with sufficient time to plan around the interruption, particularly for those who require life support equipment."
A CitiPower spokeswoman said it took its responsibility to notify customers about planned outages very seriously.
The company cancelled its planned work in Brunswick and restored power within 40 minutes as soon as it learned a life support customer was affected by that outage.
It also alerted the Essential Services Commission to the incidents and worked with the commission during its investigations.
"When we identified these incidents, we immediately reviewed what occurred and what we could improve to reduce the risk of this happening again," the CitiPower spokeswoman said.
"We have now updated our processes for auditing life support customers' addresses, introduced new checks and approvals and are investigating ways to further improve our mapping system that identifies where homes and business are connected on our network."
CitiPower has paid a total $406,824 in penalties.
The company was in 2019 also fined for failing to give customers notice of a planned power outage.