The Competition and Markets Authority says it is planning to extend protection for 4 million prepayment customers beyond the end of 2020.
The prepayment price cap was initially expected to be in place until the end of 2020 by which time the CMA said it had expected the roll-out of smart meters to be "substantially completed".
"The completed roll-out of smart meters was intended to offer greater ease of switching for customers and to drive increased competition for and engagement by prepayment customers. We have provisionally found that the delay to the roll-out programme for smart meters is significant and represents a relevant change of circumstance," the CMA said.
Calculations to the way the cap is set will also be changed.