You Do Need power plug adapter while traveling from Saint Lucia to Isle of Man.

Here is Why You Need An Adapter

The outlet and plug type used in Isle of Man are C 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

Isle of Man

In Isle of Man, outlets of type C and G are in use.

Type C

Type G