Why not a linear regulator with a heatsink functioning as a cabin heater?
Depends on how much heat 
One could be drawing 1A and the dissipation is then 23W which is quite a lot. It would be fine if attached to some part of the airframe, of course…
To those who have done research on this: did you consider the Anker chargers?
I am by no means an expert on this matter, but to me Anker seems to be a company of cheap AND quality cables, powerbanks, adapters etc. I’ve bought many of their products for general use and have never been disappointed.
I use this one in my car and so far 0 complaints:
https://www.amazon.co.uk/Anker-Charger-PowerDrive-Adapter-iPhone-Black/dp/B07PGT7LSR
Don’t know how it would perform in an aircraft.
On the topic of charging:
I’ve had issues with the SkyEcho ADS-B related to the charger used. It seems like it really doesn’t like being charged from a USB-C to USB-C cable, it only likes a “normal” USB to USB-C.
I have a MyGoFlight one and have never had any issues with it.
How to charge iPad on a 28v aircarft
Will the usual car cigarette lighter charger work to charge phone/iPad on a 28V aircarft? The aircarft has the socket to fit the charger.
All the ones I have seen work on 12-30V (trucks use 24V) but it should be written on your plug adapter.
As @mri mention yes, but be aware that many such chargers are cheap and generate noise or worse. I think there‘s a thread here somewhere that has lot‘s of feedback about what works and is recommended and what is junk. Personally, I would only use one from a aviation supplier such as Sportys or MyGoFlight, or at least a manufacturer known for quality gear.
I find this website very useful. https://lygte-info.dk/info/ChargerDCIndex%20UK.html Unfortunately he has not tested USB chargers in a while. I think (but I am not an expert) that noise on the DC output voltage is a reasonable proxy for build quality and RF noise…
There are 24/28V versions, for commercial vehicles.
Unless emissions data is available, I would simply buy the most expensive you can find. They are so cheap anyway.
The Cessna SP doesn’t have a cigar lighter or other outlet that I know about, so I carry several iPads for redundancy plus a portable battery pack which can keep one iPad with Foreflight going for 8 Hrs. Even then I’ve outflown them all and had to fall back on ‘traditional’ navigation (Panel mount KLN94) when away from controlled airspace!
