You Do Need power plug adapter while traveling from Guinea-Bissau to South Sudan.

Here is Why You Need An Adapter

The outlet and plug type used in South Sudan are C and D 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 Sudan

In South Sudan, outlets of type C and D are in use.

Type C

Type D