The electrical current in China is 220 volts, 50 cycles alternating current (AC), so most American appliances can't be used without a transformer. A universal adapter is especially useful in China, as wall outlets come in a bewildering variety of configurations: two- and three-pronged round plugs, as well as two-pronged flat sockets.
Consider making a small investment in a universal adapter, which has several types of plugs in one lightweight, compact unit. Most laptops and cell-phone chargers are dual voltage (i.e., they operate equally well on 110 and 220 volts), so require only an adapter. These days the same is true of small appliances such as hair dryers. Always check labels and manufacturer instructions to be sure. Don't use 110-volt outlets marked "for shavers only" for high-wattage appliances such as hair dryers.
Steve Kropla's Help for World Traveller's. Steve Kropla's Help for World Traveller's has information on electrical and telephone plugs around the world. .
Walkabout Travel Gear. Walkabout Travel Gear has a good coverage of electricity under "adapters." .