As a Google engineer, Leung has a ton of knowledge about power specs and has put that to use by reviewing nearly every third-party USB-C cable on Amazon.
In essence, they don’t use the USB-C charging spec, which forbids charging above five volts. Quick Charge, however, can charge at nine and 12 volts for a faster charge.
The issue isn’t out of left field. Our review of the HTC 10 noted the following:
Leung says USB-C specifications forbids Quick Charge from coexisting with the new standard. It doesn’t appear there’s any actual danger to your device, but it may be worth taking a look at if you want to ensure there’s no potential for long-term damage. And if you're invested in USB-C chargers for Nexus, Chromebook, or Macbook products, know they won't charge those two phones quickly, just at the standard rate.
The impact on you: There’s no danger that you’re going to fry your device with any of these chargers. It just means that despite how nice and reversible USB-C is, there are still some standards to be ironed out. Maybe Samsung was on to something by sticking with micro-USB for the Galaxy S7 and S7 Edge.