Direct Debit customers could also save around £60 per year by changing supplier.
The report also showed that prepayment meter householders were unaware of the financial rewards they could benefit from were they to switch.
As part of its campaign to educate prepayment meter (PPM) consumers on the options available to them, Ofgem has identified the best and worst providers for PPM. Scottish and Southern Energy offers the best deal for PPM electricity customers, it says, while npower has the worst.
"PPM customers should take advantage of the competitive market if they are to see further falls in their energy bills," Ofgem chief executive Alistair Buchanan said.
"Our research shows that by changing supplier they can save on average around £100. But in some regions this can be as great as £170 per year."
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