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

Here is Why You Need An Adapter

The outlet and plug type used in Saint Helena is G and in San Marino are C, F and L. This is how they look like.

San Marino

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

Type C

Type F

Type L

Saint Helena

In Saint Helena, outlets of type G are in use.

Type G