Electricity in Viet Nam is 220V and 50Hz. Check your appliance before your trip to see whether you need a voltage converter.
There are three main types of outlets in Viet Nam: flat blade plug, two round pins, and two parallel flat pins with ground pin. If your appliances plug is different (such as those from Australia, Austria, Germany, Italy, Hong Kong, New Zealand, Singapore) you will need a plug adapter. The adapter can be purchased from many outlets in your home country as well as at the airport.
Note that: if you plan to go to rural areas there will not be much electricity available. During the summer when demand exceeds supply, city and countryside alike may experience periods of blackout.