Apple chargers, not connected - or once the device is charged, will draw just a minute amount of electricity. Something like US$0.014 worth per YEAR (or double that in Europe where the electricity is twice as expensive)
While laudable it really isn't necessary. Chargers made by others will not necessarily give you the same results. As they say 'your mileage may (will) vary'!
And Apple Geniuses should know this. (It's easily googable)