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

Here is Why You Need An Adapter

The outlet and plug type used in South Sudan are C and D and in Nauru is I. This is how they look like.

Nauru

In Nauru, outlets of type I are in use.

Type I

South Sudan

In South Sudan, outlets of type C and D are in use.

Type C

Type D