You Do Need power plug adapter while traveling from Sierra Leone to Senegal.

Here is Why You Need An Adapter

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

Sierra Leone

In Sierra Leone, outlets of type D and G are in use.

Type D

Type G

Senegal

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

Type C

Type D

Type E

Type K