In the late nineteenth century, Edison favoured generating and supplying direct current (DC) electricity while Westinghouse promoted the use of alternating current (AC) electricity.

Edison had the initial advantage that the technology for generating DC was well established and DC worked well over short distances. However, DC could only be generated and distributed at the voltages at which it was used by consumers. This meant that currents in conductors were large, leading to huge and expensive energy losses over distances of more than one or two kilometres. To supply a large city required many power stations throughout the city and an unattractive proliferation of wires to carry the required current.
The great advantage of AC was that, through the use of transformers , the voltage could be stepped up or down as required. This meant that AC could be generated at moderately low voltages, stepped up to high voltages for transmission over great distances and stepped down again to lower voltages for consumers. The higher voltage meant that AC could be transmitted over greater distances than DC, with smaller energy losses. Power stations could be fewer and further apart and conductors could be lighter.
Competition was not always open and fair. Edison had a vested interest in DC as he owned hundreds of DC power stations and all of his many electrical inventions to that time ran on DC. Edison attempted to prove that AC was very dangerous by electrocuting animals on stage and convincing authorities to use AC for the first electric chair. He resorted to legal tactics in an attempt to have AC banned and to prevent its use with his inventions. Edison seems to have unreasonably shunned AC electricity. AC eventually came to be the dominant form in which electricity is generated world-wide.