Jan Hedlund wrote:
/.../
The mains voltage in Vietnam is 220 V AC 50 Hz, but the sockets are different. A passive plug adapter would be needed in order to use a US power adapter. Such plug adapters can often be found locally.
/.../
Addendum
Some sockets may be different. Other sockets may be of the same type as (or similar to) those used in the United States. In the latter case, an extra passive plug adapter may not be needed.
However, since the AC voltage in Vietnam is 220 V 50 Hz, it is essential that the power adapter can handle this. Again, such information should always be available on the power adapter (label/text).
Another alternative is of course to buy an appropriate power adapter with USB-C locally.