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

Brunei

In Brunei, outlets of type G are in use.

Type G

South Africa

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

Type C

Type M

Type N