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

Here is Why You Need An Adapter

The outlet and plug type used in San Marino 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

San Marino

In San Marino, outlets of type C, F and L are in use.

Type C

Type F

Type L