You Do Need power plug adapter while traveling from Brunei 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 Brunei is G. This is how they look like.

Brunei

In Brunei, outlets of type G are in use.

Type G

San Marino

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

Type C

Type F

Type L