Open Electric has ceased supplying power to 1,100 customers in Northern Ireland.
The Utility Regulator revoked the firm’s licence and accounts have been switched automatically to Power NI.
Regulator chief executive Jenny Pyper said: “We have been carefully watching market developments in general, particularly over the last few weeks and have been speaking with suppliers.
“As soon as we decided that Open Electric’s licence should be revoked, we activated established arrangements to ensure that affected customers did not lose their electricity supply and were transferred seamlessly to Power NI.
“Open Electric’s customers have now all been transferred to Power NI on the same tariff basis as Power NI’s existing customers.
“We regulate Power NI’s tariff so customers can be assured that the price they pay, reflects the actual cost of delivering electricity to their home or business.”
Customers who pay by Direct Debit or pay when they receive a bill, do not need to do anything further at present.
However, they will need to contact Power NI to set up their preferred payment option as bank details have not been passed on.
Customers who have a Pay As You Go meter will need to contact Power NI to receive a new keypad number in order to top up their meter, but their supply will not be affected.
Kerstie Forsyth from Power NI said: “We would like to assure the Open Electric customers that Power NI will look after them with no disruption to their supply.”