The mid to late 1880s saw the introduction of alternating current (AC) systems in Europe and the U.S. AC power had an advantage in that transformers, installed at power stations, could be used to raise the voltage from the generators, and transformers at local substations could reduce voltage to supply loads. Increasing the voltage reduced the current in the transmission and distribution lines and hence the size of conductors and distribution losses. This made it more economical to distribute power over long distances. Generators (such as hydroelectric sites) could be located far from the loads. AC and DC competed for a while, during a period called the War of Currents. The DC system was able to claim slightly greater safety, but this difference was not great enough to overwhelm the enormous technical and economic advantages of alternating current which eventually won out.[1]
 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.
No. When you’ve chosen a new deal, your new supplier will handle the switching process. They’ll contact you to let you know what date you’ll be transferred over, and they’ll contact you around the switching date to ask for a meter reading. They’ll pass this on to your old supplier so they can send you a final bill. You don’t need to contact your old supplier, as the new supplier will handle everything for you.
Of course, choosing a new electricity supplier or natural gas supplier does not mean you are replacing your utility. Your utility will still deliver whatever energy supply you choose, safely and reliably. Since your utility company depends on where you live, you don't have to worry about choosing a utility company. In general, utilities are responsible for maintaining the energy infrastructure. If you experience a power outage or see a downed power line, call your utility company. These are listed in the Utility Companies column below.