The regulator has banned suppliers from offering complex tariffs, for example where consumers are initially charged a higher rate, which falls the more they use.
It said the reforms were the biggest change to the retail energy market since competition was introduced in the late 1990s.
The reforms also mean that once a consumer has decided how they want to pay for energy they will have just four tariffs to choose from for gas and four for electricity, from each supplier. Together these changes will make it far easier for consumers to compare deals and find the best tariff for them, says Ofgem.
From April a range of further reforms will give consumers much clearer information on energy. For example, suppliers will have to tell consumers regularly in writing which of their tariffs is cheapest for them.
Andrew Wright, Ofgem chief executive, said: "It is getting easier for consumers to get a better energy deal and by April further help will arrive in the form of clearer personalised information. The aim is to ensure competition bears down hard on prices."