Scottish Power has become the fourth of the big six energy firms to announce price rises just in time for winter.
The giant will hit 2.3 million households with an average 7% rise in their gas and electricity prices on 3 December.
The increase will add £104 a year to a typical bill. Its 700,000 customers on fixed or capped rate deals are shielded from the rise by the nature of their tariff.
Scottish Power, like its rivals, blames rising costs at its end.
The depressing news for comes hot on the heels of Friday's madness which saw British Gas announce a 6% gas and electricity rise for 8.5 million households from 16 November and Npower reveal an 8.8% gas and 9.1 electricity rise on 26 November for three million customers.
Scottish & Southern Energy (which includes the Atlantic, Scottish Hydro, Southern Elec and Swalec brands) today increased gas & electricity bills by an average 9%.
EDF has yet to show its hand, while Eon has pledged to hold prices this year, but that gives it licence to raise them immediately on 1 January.
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Power firms have come under fire from consumer groups for raising costs for struggling households at the same time they are making bumper profits.
A report last week by the National Debtline charity found 16% of callers have energy arrears.
British Gas managing director Phil Bentley said last week the firm would "go out of business" if it didn't put prices up, as it would be making a loss.
Neil Clitheroe, Scottish Power head of retail and generation, says: "We work hard to protect our customers and we regret we've had to announce a price increase today. We reduced our gas prices in February but for most of the year we have been absorbing increased costs."
Don't moan, fix
Martin Lewis, MoneySavingExpert.com creator, says: "Four of the big six have now gone. I guess EDF will be soon, while Eon has promised to hold this year, but that probably means it'll raise prices on 1 January.
"People shouldn't simply moan about price hikes. There is still a window of opportunity to beat them.
"This is an especially important moment for those on a standard tariff. If that's you, do a comparison to find the cheapest fixed rate deal.
"Typically, you can save £200+ per year and guarantee no hikes for the next two winters. More surprisingly, in some cases you can fix with no exit fees, so you can leave if the market moves the other way."