New Twin Otters CAN be ordered with any of the previously available de Havilland special purpose modifications (cameras, scientific survey, etc.).
Why anyone would want bigger generators is beyond me. The Series 400 aircraft only consumes about 50 amps of power with all avionics working, and it already has two 200 amp generators installed. One generator alone is more than sufficient to support every electrical load operating at the same time, including full de-ice with the heated windshield, hot props, every single light bulb in the aircraft turned on, etc.
The new avionics in the aircraft draw far, far less power than the old avionics, and all of the lighting (excepting the two wing inspection lights) is either LED or high intensity xenon discharge.
Michael