You Do Need power plug adapter while traveling from Ireland (Eire) 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 Ireland (Eire) is G. This is how they look like.

Ireland (Eire)

In Ireland (Eire), outlets of type G are in use.

Type G

Marshall Islands

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

Type A

Type B