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

Saint Barthélemy

In Saint Barthélemy, 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