More than six million domestic energy customers switched their accounts last year, a 15% increase on 2014, the latest figures from regulator Ofgem show.
This is the highest number of switches since 2011, and more than 40% of them were to independents.
Ofgem consistently advises consumers that they could save hundreds of pounds by switching and has also referred the market to the Competition and Markets Authority (CMA) for a full inquiry, saying it is committed to working with the CMA to ensure the market "works better for all consumers".
While official figures show customer complaints to energy firms fell by almost a quarter last year to five million, consumer groups say this is still too high and suppliers have continued to face hefty penalties for failing to fulfil their service obligations.
Npower revealed it lost more than 350,000 customer accounts in 2015 after an "extremely difficult" year of hefty financial losses and customer service failings.
Long-running problems with its IT billing system and poor complaints handling resulted in a £26 million fine from regulator Ofgem in January.
Since the beginning of last year alone, Ofgem has also imposed penalties stretching into the millions of pounds on fellow Big Six companies E.ON, SSE, British Gas and Scottish Power.
In January, consumer group Which? renewed its criticism of the Big Six for poor levels of customer service.
The watchdog's survey of more than 8,900 people found three of the companies had below average customer satisfaction ratings while the other three were only just above average.
For the sixth year running the survey showed npower had the lowest customer satisfaction rating with 41%, closely followed by Scottish Power with 44%, while SSE, with 52%, was just below the average of 53%.
E.On with 53%, British Gas with 54% and EDF with 55% were just above the average.
For the fifth year running, the best performers were smaller companies, with OVO Energy on 82%, followed by Good Energy with 81% and Ecotricity with 77%.
Which? executive director Richard Lloyd said at the time: "Once again the smaller energy suppliers are leading the way when it comes to customer satisfaction, leaving the Big Six providers in their wake."
Ofgem senior partner Rachel Fletcher said: "It's encouraging to see switching levels at their highest level for four years.
"With more than 30 suppliers active in the energy market and hundreds of pounds of savings to be made, it's a great opportunity to shop around.
"Whether customer service, price or both is what's most important to you, remember you always have a choice. If your energy company isn't up to scratch, vote with your feet and walk away."