Domestic electricity supply voltage varies between countries. Over 30 countries (including those in North America) use a voltage of 110V~130V, while another 120 countries (including most of Europe), use a voltage of 220V~230V. The electricity in China is generally 220V, 50HZ, AC (Hong Kong is 200V; Taiwan is 110V), while the supply voltage of Japan is 110V, 60HZ.
          If you travel to China and wish to bring electric devices for use during your stay, a transformer, which can be bought in China for CNY100-200, is necessary. Most of the hotels in China have both 110V and 220V electrical outlets in the bathrooms, though in guest rooms usually only 220V sockets are available.
          As the shape of a socket varies between countries, a portable plug adaptor may also be necessary. It can be purchased from travel stores (such as Franzus) or electronics stores (i.e. RadioShack, Best Buy) in your local countries. Also you can buy it in China.

Standards of Sockets:
At present, there are five main standards of sockets in the world, including the standards of Europe, America, Britain, South Africa and China. Hereunder are the related pictures for your reference:

  European standard
This type of sockets (also called German-standard) is widely used in European countries. Plugs fit very well into such sockets, making it difficult for plugs to work loose by accident, which helps to increase safety.

 American standard
This is an American-standard socket, which is widely used in the USA, Japan, Canada and other countries.

   British standard
The British-standard socket is mainly used in Britain, New Zealand and many other countries. Also Hong Kong in China uses such a socket.

  South African standard
This is a South African-standard socket, widely used in Africa and India. The upper hole is bigger than the two lower.

 Chinese standard
Such a socket is common in China, Australia and many other countries.