Energia, which has 300,000 customers in this country, is set to hike its prices just as the colder weather sets in.
It is the third supplier this year to increase customer costs.
The energy supplier recently paid a €40m dividend to its investment fund owners.
From October 9, Energia electricity customers will be hit with a 10.9pc increase.
This will work out at a rise of €205 a year on the average bill.
Energia Dual Fuel customers are to have a 6pc increase imposed on them.
Energia is raising its prices.
Today’s News in 90 Seconds – Tuesday, September 9
Over a year, this works out at a rise of €205.
Energia Smart Meter Electricity plan customers will see a 12.1pc increase.
This will add €194 a year to the typical annual household bill.
Energia Smart Meter Dual Fuel plan customers will have a 6.2pc increase imposed from October 9, two days after the Budget.
Over a year they will be faced with paying an extra €193.
There is no change to Energia gas prices.
It said the price rises are now unavoidable due to ongoing, substantial increases in electricity system operator and network charges.
Daragh Cassidy of price comparison site Bonkers.ie said the rises were “hefty”.
“Although wholesale energy prices have reduced hugely since the height of the energy crisis in 2002, they still remain high,” he said.
Wholesale electricity prices remain around 80pc to 90pc above the level they were at before the war in Ukraine broke out. It’s similar for gas, Mr Cassidy said.
“On top of this, costs for the upkeep of the electricity grid in particular keep on rising.
“Around 30pc of the price we pay for our electricity and gas goes to Eirgrid and ESB Networks, and Gas Networks Ireland for the upkeep of the electricity and gas networks respectively.”
The focus will now be on ESB-owned Electric Ireland, which has 1.3 million customers.
Last month some 45,500 Flogas residential electricity customers were hit by a price rise of around €10.51 a month, adding €126 to annual bills.
It blamed higher network charges after it announced a rise of 7pc in electricity prices.
The standing charge for people on the standard Flogas electricity rate is rising from €257.38 a year to €275.39.
In April, SSE Airtricity raised electricity bills by 10.5pc, and gas bills by 8.4pc.
The move impacted around 250,000 electricity customers and 85,000 gas customers.
It blamed rising wholesale energy prices and higher network charges imposed by the energy regulator.
Last year, the Commission for Regulation of Utilities (CRU) hiked fees which worked out at just over €100 a year per, with further increases also likely over the following years.
The Energia price rise comes after the Government has repeatedly said there will be no energy credits in next month’s Budget. Last year the credits gave households €250 each towards their energy bills.
The credits, coupled with substantial social welfare support, had helped shield customers from high energy costs, experts said.
And the VAT rate on energy bills is due to revert back to 13.5pc, from the temporary 9pc at the moment, at the end of October, unless the lower rate is extended in the Budget.
Across all energy suppliers some 300,000 households are in arrears on their electricity bills, with 176,000 of those in arrears for 90 days or more.