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

Here is Why You Need An Adapter

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

Guinea

In Guinea, outlets of type C, F and K are in use.

Type C

Type F

Type K

Vietnam

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

Type A

Type B

Type C