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

Here is Why You Need An Adapter

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

Rwanda

In Rwanda, outlets of type C, E, F and G are in use.

Type C

Type E

Type F

Type G

Guinea-Bissau

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

Type C