You Do Need power plug adapter while traveling from San Marino to Guinea-Bissau.

Here is Why You Need An Adapter

The outlet and plug type used in Guinea-Bissau is C 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

Guinea-Bissau

In Guinea-Bissau, outlets of type C are in use.

Type C