You Do Need power plug adapter while traveling from Guinea-Bissau 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 Guinea-Bissau is C. This is how they look like.

Guinea-Bissau

In Guinea-Bissau, outlets of type C are in use.

Type C

South Africa

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

Type C

Type M

Type N