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

Here is Why You Need An Adapter

The outlet and plug type used in Guinea-Bissau is C and in Guinea are C, F and K. This is how they look like.

Guinea

In Guinea, outlets of type C, F and K are in use.

Type C

Type F

Type K

Guinea-Bissau

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

Type C