You Do Need power plug adapter while traveling from Canary Islands to Saint Lucia.

Here is Why You Need An Adapter

The outlet and plug type used in Saint Lucia is G and in Canary Islands are C, E and F. This is how they look like.

Canary Islands

In Canary Islands, outlets of type C, E and F are in use.

Type C

Type E

Type F

Saint Lucia

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

Type G