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

Here is Why You Need An Adapter

The outlet and plug type used in Vietnam are A, B and C and in South Africa are C, M and N. This is how they look like.

South Africa

In South Africa, outlets of type C, M and N are in use.

Type C

Type M

Type N

Vietnam

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

Type A

Type B

Type C