I have a 40W USB PD compliant charger from my ultrabook. I recently bought a pair of headphones (Sony WH-1000XM4) which can be charged using a USB C Plug. Sadly I can not find in the specifications of these headphones whether they support the USB PD standard. It only says they are supposed to operate at 5V and draw 1.5A, so they are potentially not compatible.

So I'm wondering, what happens when a non USB PD compliant device is charged with a USB PD source? The source can supply 5-20V. I assume the device would be fried if it were to be exposed to the full 20V, but I wonder whether the source recognize that the device is not USB PD compatible and doesn't supply any voltage at all. This would make sense to me, as it seems like USB PD compliant devices "tell" the source which voltage they want.