Compatibility summary
You will need a travel adapter in Guernsey; plug types used there differ from Mexico. Voltage differs by more than 20% — a voltage converter may be needed for some appliances.
Plug comparison
Mexico plug types: A B
Guernsey plug types: G
There is no common plug type between Mexico (A B) and Guernsey (G). You need a travel adapter.
Voltage comparison
Mexico: 127V, 60Hz
Guernsey: 230V, 50Hz
Voltage converter recommended (Mexico 127V vs Guernsey 230V).