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

Here is Why You Need An Adapter

The outlet and plug type used in Saint Barthélemy 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 Barthélemy

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

Type C

Type E