In Thailand, the voltage of domestic AC is 220 volt (50 cycles). Foreign visitors are advised to bring along travel adaptors to fit the outlets in the country. 

Electrical sockets in Thailand are compatible with both flat parallel prongs (like in the United States and Japan) and two round pins (like in most European and Asian countries). While two-pin sockets  are common in Thailand, some establishments like hotels and offices also have three-pin outlets installed. 
Visitors from countries that use 110-voltage electricity are recommended not to bring their personal 110V appliances, and instead find the 220V substitutes if possible. This is because it can be dangerous to use an electrical appliance that is rated at a different voltage from the supply.

Most 110V appliances function with 220-to-110 voltage converters (transformers) which are available at most department stores. However, there are a number of concerns surrounding the application of such tools, including: (1) issues with ground connection and electric shock; (2) the rating of the transformer must match the voltage of the appliances to which it will connect; (3) the normal operation of an 60 Hz appliance may be affected if it is used on a 50Hz supply, and (4) the transformers are often polarity sensitive.