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

Here is Why You Need An Adapter

The outlet and plug type used in South Africa are C, M and N and in Kiribati is I. This is how they look like.

Kiribati

In Kiribati, outlets of type I are in use.

Type I

South Africa

In South Africa, outlets of type C, M and N are in use.

Type C

Type M

Type N