Background information

The official Chinese hybrid socket.
History
In the past, China did not have an official plug and socket system and a wide range of different plugs and sockets were used within its borders. For a long time, the Chinese government thought this was the perfect solution (one socket for a huge variety of plugs), but heightened awareness of electrical safety hazards (universal sockets are notoriously unsafe) lead to the adoption of a national standard.
In 2009, the Chinese government eventually decided on a specific type of (safe) hybrid socket that accommodates Australian type I, American type A and European type C plugs. However, for grounded equipment, only the three-pronged type I plugs can be used. So, in other words, type I could be considered the “preferred and future-proof standard” of mainland China.
In Australasia and Argentina, type I receptacles typically have the earth contact positioned downwards, whereas in China sockets usually have the earth contact at the top.
Click here for a global map showing the spread of the different plug types used around the world.
Click here for a detailed list of the countries of the world with their respective plug and outlet types, voltage and frequency.