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

Here is Why You Need An Adapter

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

Yemen

In Yemen, outlets of type A, D and G are in use.

Type A

Type D

Type G

Vietnam

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

Type A

Type B

Type C