You Do Need power plug adapter while traveling from Fiji 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 Fiji is I. This is how they look like.

Fiji

In Fiji, 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