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

Here is Why You Need An Adapter

The outlet and plug type used in Marshall Islands are A and B 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

Marshall Islands

In Marshall Islands, outlets of type A and B are in use.

Type A

Type B