You Do Need power plug adapter while traveling from Cayman Islands 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 Cayman Islands are A and B. This is how they look like.

Cayman Islands

In Cayman Islands, 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