USB-C

More and more manufacturers of mobile phones drop the 3.5 headphone jack.
Another trend is replacing the micro USB connector with a USB-C connector.

Today you can get dongles with USB-C in and 3.5 analog out.

This means there is a DAC build-in.

A perfect solution to connect wired headphones to your mobile that lacks the analog jack.

However, there is also a USB-C Audio Adapter Accessory Mode.

In this mode the device sends analog audio over the USB!

All you need is a passive adapter.

Obvious, USB-C is the most analog sounding digital bus!

To the best of my knowledge, there is nothing you can do as a user to invoke Audio Adapter Accessory Mode or avoid it. This explains why a passive USB-C - headphone adapter works on some mobiles but not on others. The same applies to USB DAC's.

A bit more about USB and this Audio Adapter Accessory Mode can be found here.

List of USB-C adapters