You Do Need power plug adapter while traveling from Saint Lucia to Sint Maarten.

Here is Why You Need An Adapter

The outlet and plug type used in Sint Maarten are A and B 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

Sint Maarten

In Sint Maarten, outlets of type A and B are in use.

Type A

Type B