You Do Need power plug adapter while traveling from Western Sahara to Saint Helena.

Here is Why You Need An Adapter

The outlet and plug type used in Saint Helena is G and in Western Sahara are C and E. This is how they look like.

Western Sahara

In Western Sahara, outlets of type C and E are in use.

Type C

Type E

Saint Helena

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

Type G