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

Here is Why You Need An Adapter

The outlet and plug type used in Tuvalu is I and in Guinea-Bissau is C. This is how they look like.

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

Type C

In Tuvalu, outlets of type I are in use.

Type I

I am from

going to