You Do Need power plug adapter while traveling from Sierra Leone 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 Sierra Leone are D and G. This is how they look like.

Sierra Leone

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

Type D

Type G

Marshall Islands

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

Type A

Type B