You Do Need power plug adapter while traveling from Vatican City 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 Vatican City are C, F and L. This is how they look like.

Vatican City

In Vatican City, outlets of type C, F and L are in use.

Type C

Type F

Type L

French Guiana

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

Type C

Type D

Type E