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

Here is Why You Need An Adapter

The outlet and plug type used in Yemen are A, D and G 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

Yemen

In Yemen, outlets of type A, D and G are in use.

Type A

Type D

Type G