You Do Need power plug adapter while traveling from Madeira 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 Madeira are C and F. This is how they look like.

Madeira

In Madeira, 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