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

Here is Why You Need An Adapter

The outlet and plug type used in Congo are C, D and E 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

Congo

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

Type C

Type D

Type E