You Do Need power plug adapter while traveling from Puerto Rico to Saint Martin.

Here is Why You Need An Adapter

The outlet and plug type used in Saint Martin are C and E and in Puerto Rico are A and B. This is how they look like.

Puerto Rico

In Puerto Rico, outlets of type A and B are in use.

Type A

Type B

Saint Martin

In Saint Martin, outlets of type C and E are in use.

Type C

Type E