It depends. USB-C supports PPS, which allows the charged device to request a specific voltage, so conversion is no longer needed.
The specification does mandate that the device must be able to fall back to a static voltage if the charger does not support PPS, though. But in practice a device could totally require PPS for fast charging, and only do trickle charging with a non-PPS charger.
> But in practice a device could totally require PPS for fast charging, and only do trickle charging with a non-PPS charger.
Not sure we have the same terms. Trickle charging is 0.02-0.05C charging to see if the charger can get the battery safely from being overdischarged to say 3V where it can start normal CC charging phase.
That would probably piss off a lot of users and the EU if not even normal charging was supported by a device connected to any USB charger, because that's back to requiring a specific charger for each device, where not even basic things that all users expect work anymore with all conforming chargers.
