You Do Need power plug adapter while traveling from Switzerland to Vietnam.

Here is Why You Need An Adapter

The outlet and plug type used in Vietnam are A, B and C and in Switzerland are C and J. This is how they look like.

Switzerland

In Switzerland, outlets of type C and J are in use.

Type C

Type J

Vietnam

In Vietnam, outlets of type A, B and C are in use.

Type A

Type B

Type C