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

Samoa

In Samoa, 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