If the monitor (or any other load, for that matter), is functioning correctly, you cannot have "too much" amperage (current). The load will only draw as much current as it needs, despite the battery being able to supply more.
BTW, can someone translate "wall wort" to Australian English?? I think you mean a socket outlet, but I'm not sure... And is it 12V AC, or DC?
EDIT: I think I realise... a small DC plugin supply.