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

Here is Why You Need An Adapter

The outlet and plug type used in Saint Helena is G and in Senegal are C, D, E and K. This is how they look like.

Senegal

In Senegal, outlets of type C, D, E and K are in use.

Type C

Type D

Type E

Type K

Saint Helena

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

Type G