Times change. Back when I was doing a lot of Mac consulting, I bought an inverter for my car so that I could convert the 12V power in the vehicle to 120V AC to charge my MacBook Air between appointments. It was bulky, hot, and slow. Fast-forward to 2017, when a tiny box from GearMo ($22.95 from Amazon, Model GM-UCPDCARB) can provide 60W of USB Type-C power to my MacBook Pro and charge one other device through another USB-A port that uses Qualcomm's Quick Charge 3.0 protocol.
This charger was released on 10/1/17 to provide a total of 75W of charging power. As noted above, the USB-C connector can pump 60W to your MacBook or MacBook Pro to charge it up fast, while the other port can either provide 15W at 3A, or use Qualcomm's QC 3.0 at 12V/1.5A, 9V/2A or 5V/2.4A.
The charger -- like most car chargers these days -- plugs right into your accessory power port and when it's delivering power an LED shines to confirm that fact. I was quite impressed with how quickly this little charger could power up my 13-inch MacBook Pro during a "test drive".
Unlike a lot of the companies that supply us with gear to review, Gearmo has a US division based in Florida, and you can actually call them (toll-free or directly) for support. They also made their support email easy to find on the Gearmo website (at the top of the page!), so if you have any questions or concerns, you shouldn't have any problems contacting the company quickly.
You can also get a product manual, technical data sheet, and the FCC certification documents directly from the product page. That level of openness is really rare in the tech business, and I wish that other companies would follow GearMo's lead.