The Labour leader's remarks came as almost £1 billion was wiped off shares in Centrica - British Gas's holding company - which fell by 5.3% in trading over the course of the day. Shares in Swalec owner SSE also fell 5.8%.
Sir Roger Carr, the Centrica chairman, said: "We are all concerned about rising prices and the impact on consumers but we also have a very real responsibility that we find supplies to make sure the lights stay on."
Asked about power blackouts, Mr Miliband said last night: "I don't think it's going to happen. This is scare stories. The real thing that shapes investment decisions in energy is the long-term framework."
He said what had grabbed the attention of the industry was the price freeze up to the beginning of 2017, which would save households £120 a year and businesses £1800, but cost energy firms a total of £4.5bn.
"It's in the interests of the companies to reset the market and restore public confidence," declared the Labour leader.
"Having a clear commitment on taking the carbon out of energy by 2030 will help investment because it gives certainty to the companies. Some of the other proposals we've made will provide that long-term certainty the market needs."
He added: "It's in the interests of the companies themselves to have a new system put in place, restore public confidence and sort out the market."
During a conference Q&A, Mr Miliband urged David Cameron to "stop ducking and diving" on the pre-General Election TV debates.
He later said: "Let's have election TV debates with the three party leaders. I'm happy with the same format as last time. Let's have those debates."
Elsewhere, the Labour leader said his wife Justine had been a great support and she would be supporting him publicly at the next election.