You Do Need power plug adapter while traveling from Saint Martin 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 Saint Martin are C and E. This is how they look like.

Saint Martin

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

Type C

Type E

French Guiana

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

Type C

Type D

Type E