You Do Need power plug adapter while traveling from Mongolia 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 Mongolia are C and E. This is how they look like.

Mongolia

In Mongolia, outlets of type C and E are in use.

Type C

Type E

San Marino

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

Type C

Type F

Type L