You Do Need power plug adapter while traveling from French Guiana to El Salvador.

Here is Why You Need An Adapter

The outlet and plug type used in El Salvador are A and B 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

El Salvador

In El Salvador, outlets of type A and B are in use.

Type A

Type B