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

Here is Why You Need An Adapter

The outlet and plug type used in Guinea-Bissau is C and in Yemen are A, D and G. This is how they look like.

Yemen

In Yemen, outlets of type A, D and G are in use.

Type A

Type D

Type G

Guinea-Bissau

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

Type C