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

Belgium

In Belgium, 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