The sockets in Vietnam are all round holes, and the voltage is the same. If your mobile phone is also a round hole, you don't need to bring a converter, but if the mobile phone charger is flat and has three plugs, you need to use a converter.
Extended data:
Asia Pacific region?
Area name (Chinese/English), voltage, frequency and plug shape
China/China: 220V, 50, DC, two feet/splay.
Vietnam/Vietnam: 120/220v, 50Hz, A.B.E.G. Round feet and flat feet.
References:
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