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

Here is Why You Need An Adapter

The outlet and plug type used in Bermuda are A and B 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

Bermuda

In Bermuda, outlets of type A and B are in use.

Type A

Type B