The many different plugs and standards across the countries make it necessary to check labels to reduce the risk of accidentally buying the wrong adapter or forgetting an essential converter.
A few important variations in standards between countries (or sometimes even within a country) include differences in:
The two primary standards for current are Alternating Current and Direct Current. The U.S. standard was developed during the famous war between Tesla and Edison. Edison favored DC, and Tesla preferred AC. The big advantage to AC is that it is capable of traveling greater distances between power stations, and in the end, it was the standard that won out in the U.S.