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

Here is Why You Need An Adapter

The outlet and plug type used in Cuba are A, B, C and L and in El Salvador are A and B. This is how they look like.

El Salvador

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

Type A

Type B

Cuba

In Cuba, outlets of type A, B, C and L are in use.

Type A

Type B

Type C

Type L