You Do Need power plug adapter while traveling from Saint Barthélemy to Cuba.

Here is Why You Need An Adapter

The outlet and plug type used in Cuba are A, B, C and L and in Saint Barthélemy are C and E. This is how they look like.

Saint Barthélemy

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

Type C

Type E

Cuba

In Cuba, outlets of type A, B, C and L are in use.

Type A

Type B

Type C

Type L