You Do Need power plug adapter while traveling from Cape Verde to Saint Lucia.

Here is Why You Need An Adapter

The outlet and plug type used in Saint Lucia is G and in Cape Verde are C and F. This is how they look like.

Cape Verde

In Cape Verde, outlets of type C and F are in use.

Type C

Type F

Saint Lucia

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

Type G