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

Here is Why You Need An Adapter

The outlet and plug type used in Balearic Islands are C and F and in Channel Islands (Guernsey & Jersey) are C and G. This is how they look like.

Channel Islands (Guernsey & Jersey)

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

Type C

Type G

Balearic Islands

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

Type C

Type F