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

Here is Why You Need An Adapter

The outlet and plug type used in Vatican City are C, F and L and in French Guiana are C, D and E. This is how they look like.

French Guiana

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

Type C

Type D

Type E

Vatican City

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

Type C

Type F

Type L