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

Here is Why You Need An Adapter

The outlet and plug type used in Niger are C, D, E and F 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

Niger

In Niger, outlets of type C, D, E and F are in use.

Type C

Type D

Type E

Type F