You Do Need power plug adapter while traveling from Croatia to Saint Kitts and Nevis.

Here is Why You Need An Adapter

The outlet and plug type used in Saint Kitts and Nevis are D and G and in Croatia are C and F. This is how they look like.

Croatia

In Croatia, outlets of type C and F are in use.

Type C

Type F

Saint Kitts and Nevis

In Saint Kitts and Nevis, outlets of type D and G are in use.

Type D

Type G