Electric current in Vietnam is 220 Volts 50 Hz. The usual voltage is between 220V and 240V, 50 cycles; but sometimes you encounter 110V, also at 50 cycles, just to confuse things.
Two-pin (ungrounded) plug is more popular than three-pin one. If you have any devices needing a special outlet, please bring its adapter kit. The best investment is a universal AC adapter, which will enable you to plug it in anywhere without frying the innards.
Tap water in urban areas in Vietnam is chlorinated, but it is recommended that it should be boiled before drinking.