Scottish & Southern Energy said it had added 600,000 new customers in the past year by showing 'restraint' on prices.
The group, which owns Southern Electric, Scottish Hydro Electric and Swalec in Wales, announced price rises in March but said at the time it would leave tariffs unchanged until at least the start of 2007.
The company said it would continue to protect customers from recent volatility in wholesale energy markets.
This was despite rival Scottish Power announcing last week that price rises were "unavoidable" and British Gas owner Centrica warned its residential arm was still making a loss.
SSE had 6.7 million customers in its energy-supply business at the end of March after adding 600,000 customers during the past financial year and 2.2 million customers since the start of 2002.
Only Centrica and Power-Gen have more customers on their books.
"We think the whole the issue of pricing is one of balance between the interests of shareholders and customers," said chief executive Ian Marchant.
"It depends on your hedging position and we're very comfortable that we can make that promise."
The growth in customer numbers helped SSE's generation and supply business to increase operating profits by 14.5 per cent to £444.8 million - a performance which was helped by the £260 million acquisition of the Ferrybridge and Fiddler's Ferry power stations in 2004.
SSE said the return on coal had been so good it was now looking at building a new, more environment-friendly 500 megawatt plant at Ferrybridge in northern England.
Across the group, profits were up in line with expectations to £858.2 million, a rise of 19 per cent on a year earlier.
Growth was achieved in all of its operating divisions, including the company's regulated power distribution and transmission arm and in gas storage through the UK's largest onshore facility at Hornsea in East Yorkshire.
The gas storage business posted profits of £27.3 million - up 43.7 per cent as demand for such facilities remained high in a volatile gas market and in light of a fire at Centrica's Rough site in the North Sea earlier this year.
In power generation, SSE offset the impact of high winter fuel costs through its diverse portfolio of assets relying on hydro, coal, gas, oil, and wind. It is responsible for more than 10,000 megawatts of generation capacity.
And the company expanded its investment in renewable sources after announcing it had entered into an agreement to buy two wind farm developments at Toddleburn in the Scottish Borders and Calliacher in Perth and Kinross.
SSE already owns and operates four wind farms in Scotland with a total capacity of 162 megawatts.
"SSE continues to benefit from its operational efficiency, diverse fuel fleet and focus on offering good service at a low cost," Cazenove analyst Edmund Reid said in a note.
SSE proposed a full-year dividend up 9.4 per cent at 46.5 pence per share