Powering laptop from 12V sources without inverter

Yes, tons of power is wasted going from 12V to 110V, especially when all you do is to stick it into a psu which also loses some power turning it back into low voltage DC.

You can buy a DC/DC converter which will deliver a 9-20 V DC adjustable voltage when given 10-24 V DC input.

I've built a SEPIC style converter before, for just this sort of thing: http://dren.dk/carpower.html

Some laptops can run off variable power sources, usually older ones.

DC-DC adapters lose 20% in their basic conversion from 12V to 19V.(Tested myself with multimeter), vs 40+% or more to power 110V inverter to run AC adapter to output 19VDC.

I would like to find a newer already EFFICIENT laptop that has been built to take a 11-15.5V DC power input... One older computer I do have(too slow) is a NEC Daylite, 16V powersupply usually but it will run off 11-16V no problem. about 7-11Watts depending on usage.

Update: Some modern laptops are powered from USB-C instead of a dedicated power jack. These laptops can be recharged directly from a USB-C car "cigarette lighter" power adapter, which operates DC-DC rather than DC-AC-DC.

Looks like they typically max out at 30W per port. This should still work, more slowly than approx. 90W from wall AC power adapter.

Examples from Anker: https://www.anker.com/products/108/204/car-chargers

For older models, it's possible your laptop manufacturer already has an auto/airplane vehicle adapter accessory that you can buy. It will convert the battery voltage to the proper input voltage for the laptop directly (DC-DC). Perhaps it will serve double duty and be able to take AC (wall) input as well.

Another option would be a generic car adapter that has interchangeable plug tips to fit most major laptop brands.