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

Here is Why You Need An Adapter

The outlet and plug type used in Sierra Leone 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

Sierra Leone

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

Type D

Type G