I’m not sure if this is the right place to put this but well…here it is. I’ve tried a few options before with mixed success. A £3 usb buck converter with built in lcd and usb port that got really hot, melted part of the pcb and then started smoking abd various other cheap dc step downs that only work for android phones or 12v lights.
This way works, is reliable, and most of all is safe. I wired in a Fulree DC-DC 15-55v to 12v 3A max converter in parallel to the vesc circuit. I put in a push button lactching switch so I can turn it on and off even when the board isn’t on and used an inline fuse which I got off of a 12v motorcyle waterproof usb adapter which is what teh Fulree is outputting to. The perks of having this is A) It already comes with an inline fuse that is easily swapped should anything go wrong and B) it has an SAE connector which means it’s easy to disconnect it if and when I want ot take the case off. C) the USB plug has a waterproof cover Here is a link https://www.amazon.co.uk/MICTUNING-Disconnect-Waterproof-Motorcycle-Cellphone-SAE-USB-Adapter-Extension-Cable/dp/B01MSK7ZAV/ref=pd_lpo_sbs_263_img_1?_encoding=UTF8&psc=1&refRID=9VS1KC5GTBE8KWMRA7WR
Here is a pic of the push button switch and also for anybody that has epoxied their XT90 into the case this is how I got round not being able to take the case off.