Electricity was first channelled into homes for lighting, and since then it has become a staple ingredient for heating, cooling, cooking, entertainment and even security.
Originally some home appliances got their power by connecting directly to the light socket. Because more and more home appliances needed to be connected and at higher voltage, the two prong electric outlet started appearing from the 1920s. As safety became an issue, a third pin was added which was connected to earth so that in the event of a short circuit the fuse would blow and disconnect supply.
The main reason why there are so many different styles of plugs and outlets is because no one adopted a standard, each country preferring to make their own versions and improvements. Many countries still do not have as standard the three prong plug. For many decades the International Elecrotechnical Commission has pushed for a universal domestic plug, but politics and money have always resisted adoption. Only Brazil has began using this proposed standard plug.
The current system of alternating current generation and distribution was invented by Nicola Tesla. He calculated that 60Hz was the best frequency for generating power and favoured 240 volts. His rival Thomas Edison disagreed as his developing direct current system was 110 volts. Originally Europe’s power was 120V like Japan and USA is today. In the 1950s it was decided that more power was needed so Europe doubled their voltage but the US decided it was too expensive for everyone to replace their appliances - at that time almost all US homes had major appliances whereas in Europe they did not, hence the US remained with 120V.
For the majority of travel purposes these are the main plug types you will need to find adapters for:
USA, Canada, Mexico and Japan
Europe, South America and Asia
Some countries use slight adaptations on the European plug for their sockets (for example Italy, France, Russia and Switzerland), however you will find with these variations the European-style plug will work. Perhaps surprisingly the most unsafe plug type is also the most widespread and useable throughout the world! And lucky us – along with Oceania, Argentina have adopted our angled prong plug type.