You Do Need power plug adapter while traveling from Bulgaria 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 Bulgaria are C and F. This is how they look like.

Bulgaria

In Bulgaria, outlets of type C and F are in use.

Type C

Type F

French Guiana

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

Type C

Type D

Type E