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

Here is Why You Need An Adapter

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

Solomon Islands

In Solomon Islands, outlets of type G and I are in use.

Type G

Type I

Vietnam

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

Type A

Type B

Type C