Brilliant Energy - which supplied gas and electricity to 17,000 households - has ceased trading, marking the latest casualty in the sector this winter.
The business, based in Gosforth, had boasted of providing a "straightforward" service at a "fair and stable" price.
Its collapse means energy regulator Ofgem has had to step in again to protect supplies to customers.
Brilliant is one of 10 UK suppliers to collapse in the last year.
As with the other failures, the regulator will ensure that no households have their gas or electricity cut off, and will move these customers automatically to a new supplier.
However, it cannot guarantee that the tariffs they were paying will be as cheap under the new arrangements.
Brilliant Energy also ran services under the Northumbria Energy brand. Its website said it was no longer taking customers.
Philippa Pickford, Ofgem's director for future retail markets, said: "Our message to energy customers with Brilliant Energy is there is no need to worry, as under our safety net we will make sure your energy supplies are secure and your credit balance is protected."
She said that customers should not switch for the time being. "We will update you when we have chosen a new supplier, who will then get in touch about your new tariff," she said.
"We have seen a number of supplier failures over the last year and our safety net procedures are working as they should to protect customers."
Cash-flow and rising wholesale prices have been an issue for many of them.
Those failures and the date of collapse include:
- National Gas and Power - July 2018 (80 non-domestic customers)
- Iresa - July 2018 (100,000 domestic customers)
- Gen4u - September 2018 (500 domestic customers)
- Usio Energy - October 2018 (7,000 domestic customers)
- Extra Energy - November 2018 (108,000 domestic and 21,000 business customers)
- Spark Energy Supply Limited - November 2018 (290,000 domestic customers)
- OneSelect - December 2018 (36,000 domestic customers)
- Economy Energy - January 2019 (235,000 domestic customers)
- Our Power - January 2019 (38,000 domestic customers)
Cosi Mockett, from auto-switching site Switchcraft, said that with so many customers moving to suppliers and tariffs they had not chosen "the industry is in crisis and the regulator needs to step in".
Ofgem has said there is "room for improvement" in the licensing regime so businesses are properly vetted before they start competing for customers.
New, tighter rules are expected to come into force next month.
Matthew Vickers, chief executive at the Energy Ombudsman, said: "The collapse of an energy supplier can be a stressful and unsettling experience for consumers. If you are a Brilliant Energy customer, we would echo Ofgem's advice to sit tight and don't switch.
"We are keen to work with whichever supplier is appointed to take on Brilliant Energy's customers in order to find the best possible outcome for the small number of consumers who have a complaint about the failed company open with us."