You Do Need power plug adapter while traveling from Nauru 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 Nauru is I. This is how they look like.

Nauru

In Nauru, outlets of type I are in use.

Type I

Guyana

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

Type A

Type B

Type D

Type G