You Do Need power plug adapter while traveling from Saint Lucia 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 Saint Lucia is G. This is how they look like.

Saint Lucia

In Saint Lucia, outlets of type G are in use.

Type G

El Salvador

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

Type A

Type B