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

Here is Why You Need An Adapter

The outlet and plug type used in Dominica are D and G and in Marshall Islands are A and B. This is how they look like.

Marshall Islands

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

Type A

Type B

Dominica

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

Type D

Type G