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

Here is Why You Need An Adapter

The outlet and plug type used in Guyana are A, B, 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

Guyana

In Guyana, outlets of type A, B, D and G are in use.

Type A

Type B

Type D

Type G