You Do Need power plug adapter while traveling from Tuvalu to French Guiana.

Here is Why You Need An Adapter

The outlet and plug type used in French Guiana are C, D and E and in Tuvalu is I. This is how they look like.

Tuvalu

In Tuvalu, outlets of type I are in use.

Type I

French Guiana

In French Guiana, outlets of type C, D and E are in use.

Type C

Type D

Type E