You Do Need power plug adapter while traveling from São Tomé and Príncipe to Somaliland.

Here is Why You Need An Adapter

The outlet and plug type used in Somaliland is G and in São Tomé and Príncipe are C and F. This is how they look like.

São Tomé and Príncipe

In São Tomé and Príncipe, outlets of type C and F are in use.

Type C

Type F

Somaliland

In Somaliland, outlets of type G are in use.

Type G