You Do Need power plug adapter while traveling from Nepal to Nauru.

Here is Why You Need An Adapter

The outlet and plug type used in Nauru is I and in Nepal are C, D and M. This is how they look like.

Nepal

In Nepal, outlets of type C, D and M are in use.

Type C

Type D

Type M

Nauru

In Nauru, outlets of type I are in use.

Type I