What is the advantage of a 12 volt dc power supply for in-seat power on aircraft. Most cell phones, laptops and medical equipment such as CPAP have universal power adapter (operating on 110-240 Volt ac supply). My CPAP has a universal power adapter too even though it works on 24 Volt dc. The power asupply adapter (brick) can run on 50/60Hs, as well as 400 Hz supply, which is typically found on aircraft. Laptops typically run on 12-20 volts dc.

For a gadget that consumes, say, 70 watts, 110 V ac would require less than an amp of current, while a 12 volt dc supply would draw 6 amps. Moreover, you need an extra piece of equipment to convert 12 volt dc to whatever voltage your equipment runs on.

The manual for my CPAP says that it can be used with 12 volts dc sources such as automotive and marine batteries, but not with 12 volts dc supply, that;s being charged by an ac source, which would be the case on aircraft.
Yet, some airlines provide only 12 volts dc inseat power in seats where power is not already provided, such as in Business Class or Premium economy class. Whether they provide 12v dc or 110 ac, eventual power and or current draw on the aircraft power generation system would be the same. So why do some airlines insist open providing only 12 volt dc power in cases of special request? Won't 6 amp draw between the 12 volt dc power supply and the equipment be more hazardous than less than an amp draw? What am I missing?