When it comes to the electricity itself, there is no difference at all. A cheap electric supply is the same electricity, it's simply provided by a new supplier (unless you opt for green energy - more on that here). As suppliers buy and generate different sets of energy they also have different prices. What's more, you might be on a tariff that is simply more expensive, such as a standard tariff. If you decide to switch electricity don't equate a lower price with worse service.
1. Contracts: Before, there were no contracts. You signed up or you didn’t. When it’s the only game in town, you have to play by their rules. Nowadays, you’ll see these ultra-fabulous rates bandied about but it’s only by carefully scrutinizing the fine print that you’ll discover those wonderful rates come with a one-year lock-down or other catches.