The electrical current in China is 220 volts, 50 cycles (The US is 120/60). If your appliances are not dual voltage (110/220V) you will need a voltage converter or transformer, which can be purchased in China but may be hard to find. If you bring such appliances, we recommend that you bring a voltage converter from home.
However, the best plan is to purchase local appliances (such as a hair dryer) which use the correct Chinese electrical current after you arrive, rather than bring appliances from home. The most common outlet is the one pictured in the upper right hand corner of the following link: http://www.kropla.com/china_power.htm. This outlet is common in newer buildings. Please note that power strips allowing you to plug in your computer and other hardware of variously pronged plug types are readily available at many stores and they are inexpensive. These are not power adaptors, but they do allow you to plug in almost anything.