You Do Need power plug adapter while traveling from Cuba to Channel Islands (Guernsey & Jersey).

Here is Why You Need An Adapter

The outlet and plug type used in Channel Islands (Guernsey & Jersey) are C and G and in Cuba are A, B, C and L. This is how they look like.

Cuba

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

Type A

Type B

Type C

Type L

Channel Islands (Guernsey & Jersey)

In Channel Islands (Guernsey & Jersey), outlets of type C and G are in use.

Type C

Type G