Chief executive Jonathan Brearley insisted measures were in place to cope but admitted he could not guarantee against supplies taking a hit.
He said: “Ofgem, with the industry, will do everything we can to protect customers.”
“That means putting strict rules in place around how customers are treated, making sure the price cap is set fairly but also making sure these companies are more resilient.”
Mr Brearley did not detail how rationing might work, but it has previously been suggested energy-intensive businesses could be the first to be hit, with limits on power usage.
He said in the unlikely case that domestic power supply was affected, it could be limited to short power outages in the early hours.
Mr Brearley said the changes in wholesale costs are “dramatic” and the war in Ukraine is driving up the pressures and still expects the price cap to hit around £2,800 in the autumn.
At the moment, if a company goes bust customers end up covering the costs. Under the plans, consumers’ money will better protected from future energy supplier failures.
Companies will be required to have enough working capital in the bank to ensure they can function.
Ofgem wants to put an end to customers’ credit balances “being used by some suppliers like an interest-free company credit card.”