I think you need a multi-way adapter between the socket in your car and the DJI charge lead.
The earlier / cheaper adapters came with just 2, or 3, or 4, sockets, the same as in the car. Thus you needed another adaptor to convert one of those 12 volt sockets to a 5V USB socket.
Later multi-way adaptors have one or two 5v USB sockets and two or three of the 12 volt sockets in the same housing. These are clearly more suited to your requirements.
At least, that's the situation in the UK
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Edited 2 hours later to say that arguably the better solution is to buy a mains inverter, run that from the 12v socket and always use your mains power unit that has two USB outlets, and powers the charger.
The label on the (UK) power unit isn't that exact, showing the Input as 100 / 240 volts, but only one current rating of 1.4A
I would expect more current to be required when running at 110 volts, and if that's what the 1.4A refers to I'd say an inverter rated to supply 150 or 200 watts would be fine.
For the maximum headroom, assume the 1.4A refers to running at 240 volts, for which an inverter rated at 350 watts would be fine.
You are in Australia, I am not; PLEASE do read the label on your power unit, and make any decision on inverter rating based on what it says (Volts x Amps, then round up to the nearest 50).
Regards.