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

Here is Why You Need An Adapter

The outlet and plug type used in Sierra Leone are D and G and in Saint Lucia is G. This is how they look like.

Saint Lucia

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

Type G

Sierra Leone

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

Type D

Type G