I use the device to charge an e-scooter via the car lighting system.
Firstly, this unit CANNOT provide 400W. The input is fused at 15A which means 180W in. If well designed you should be able to get ~130W out. Not the case. Tested with multiple loads and adjusted the current trimmer up and down. The best I could get was around 1A @24V out which is a measly 24W. A far cry from the advertised output. Useless.