To convert 12VDC to 240VAC for the car, I have bought a 220W inverter for ~8€ and a cigarette lighter socket for 1.50€. Basically, I just wanted to have USB-PD but the 12V to USB-PD converters are all buck converters (at least the ones I've tested) - as step-up to 24V is more expensive, it is advisable to just step up to 240VAC directly.

Note: See other stuff you can get for your car

Do not forget to at least make a knot in the cable as strain relief (which is still the quick&dirty method).

#TODO: add oscilloscope measurements