It's the cable that they include with the iPhone that has a USB connector on the charger end and a lightning port on the phone end.
That included cable allows you to charge with any manufacturer's USB-C charger in the same way that the previous version of the cable worked with any USB-A charging port.
So, in summary, the cable Apple gives you works with other manufacturers chargers, and the charger Apple gives you works with other phones, using a standard USB-C cable that, I would imagine, came with the phone.
If they want to force Apple's hand specifically, they should be focusing on the port on the phone, not the charger.