You Do Need power plug adapter while traveling from Congo 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 Congo are C, D and E. This is how they look like.

Congo

In Congo, outlets of type C, D and E are in use.

Type C

Type D

Type E

South Africa

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

Type C

Type M

Type N