You Do Need power plug adapter while traveling from Grenada 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 Grenada is G. This is how they look like.

Grenada

In Grenada, 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