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

Here is Why You Need An Adapter

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

Switzerland

In Switzerland, outlets of type C and J are in use.

Type C

Type J

Guinea-Bissau

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

Type C