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

Here is Why You Need An Adapter

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

South Sudan

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

Type C

Type D

Kiribati

In Kiribati, outlets of type I are in use.

Type I