You Do Need power plug adapter while traveling from Niger to San Marino.

Here is Why You Need An Adapter

The outlet and plug type used in San Marino are C, F and L and in Niger are C, D, E and F. This is how they look like.

Niger

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

Type C

Type D

Type E

Type F

San Marino

In San Marino, outlets of type C, F and L are in use.

Type C

Type F

Type L