[choosegoose]

Your headphones would need a DAC if you want to charge your phone and use the headphones at the same time.

Ideally you would be able to use a splitter that would male USB-C on one end and female 3.5mm + female USB-C. Unfortunately you'll be stuck with only 500mA.

The USB-C spec calls for the negotiation of power delivery (amperage) via two lines that are used for audio passthrough. When those lines are occupied the device will only pull 500mA from the cable to ensure components aren't fried.

Now if your splitter had a DAC, you could get full power but it sucks you have to spend money to listen to audio and charge your phone at the same time.

From USB Type-C Specification Release 1.3:

Analog audio headsets are supported by multiplexing four analog audio signals onto pins on the USB Type-C™ connector when in the Audio Adapter Accessory Mode. The four analog audio signals are the same as those used by a traditional 3.5 mm headset jack. This makes it possible to use existing analog headsets with a 3.5 mm to USB Type-C adapter. The audio adapter architecture allows for an audio peripheral to provide up to 500 mA back to the system for charging.