You Do Need power plug adapter while traveling from Benin 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 Benin are C and E. This is how they look like.

Benin

In Benin, outlets of type C and E are in use.

Type C

Type E

Marshall Islands

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

Type A

Type B