That might be difficult to achieve - AC/AC are not just as flexible as Switching AC/DC - usually there's just the transformer and in rare cases, low-pass filter.
Plugging 110V adaptor into 220V outlet result in doubling the voltage output - to alleviate that, you'd need dual-winding which would make the adaptor much heavier.
Better choice would be to convert O2 to accept DC voltage (3-pin power jack .. +20V, -20V and GND). Such mod would allow the use of switching adaptors.