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

Here is Why You Need An Adapter

The outlet and plug type used in Eritrea are C and L and in Nauru is I. This is how they look like.

Nauru

In Nauru, outlets of type I are in use.

Type I

Eritrea

In Eritrea, outlets of type C and L are in use.

Type C

Type L