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

Here is Why You Need An Adapter

The outlet and plug type used in Saint Martin are C and E 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

Saint Martin

In Saint Martin, outlets of type C and E are in use.

Type C

Type E