DC Port vs. AC Outlet for Running a CPAP: Which Gets More Runtime?
Running a CPAP through a power station's DC port (using a DC-to-CPAP adapter cable, if your machine supports it) generally extends runtime compared to using the AC outlet, because it bypasses the power station's internal inverter — the same inverter that otherwise converts the battery's native DC power to AC and back to DC inside the CPAP itself, a conversion that wastes some energy as heat at each step.
This is a genuinely useful, if lesser-known, trick for anyone trying to maximize a CPAP's runtime on limited battery capacity.
Why the AC route involves an unnecessary conversion
A power station's battery stores DC power, its inverter converts that DC to AC for the outlet, and then the CPAP's own internal power supply converts that AC right back to DC to actually run its motor and electronics — each conversion step loses some energy as heat, so going DC-to-DC directly (skipping the inverter) avoids one whole layer of that loss.
What you need to use the DC route
Not every CPAP supports a direct DC input, and if it does, it typically requires a specific DC adapter cable matched to both your CPAP model and the power station's DC output connector — check your CPAP manufacturer's accessories for a DC power cable option if maximizing runtime matters to you.