i looked several places for an answer to this question and couldn’t find one, so I did a little experimenting. The question is: How much more efficient is a dc-dc adapter versus going from 12 volts to 120 volts through an inverter, and then back to laptop voltage through an ac charging cord? I have a Panasonic CF-30 Mk3 Toughbook, a 150 watt dc to ac modified sine wave inverter, a Lind dc to dc converter, and two ac charging cords, one OEM Panasonic and one cheap ebay charger. I tried them all together and here’s what I found out... Charging the laptop from a 50% discharged laptop battery with the unit turned off... Panasonic Charger with inverter 3.0 amps Cheap charger with inverter....also 3.0 amps Lind dc to dc: 2.5 amps Laptop turned on and “thinking”...ie hard drive running, processor processing: Panasonic ~4.5 amps Lind: ~4.2 amps Hard to get a solid number because the amperage jumps around a lot. Laptop on but idle: Panasonic: not tested. Lind: 3.0 amps The difference is pretty insignificant if you’re charging from your car, but charging from a battery pack or from a solar power system a half an amp can make a big difference. Hope that helps.