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

Here is Why You Need An Adapter

The outlet and plug type used in Guinea-Bissau is C and in Brazil are C and N. This is how they look like.

Brazil

In Brazil, outlets of type C and N are in use.

Type C

Type N

Guinea-Bissau

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

Type C