[crote]

Because USB-C does not have a defined "upstream" and "downstream" side of the cable, a user could connect two chargers together. This is obviously a bad idea.

To prevent this, a USB-C charger is only allowed to provide power on the cable once it senses a downstream device on the other side. A legacy USB-A to USB-C cable always applies power, though, as this does not provide any danger.

Some low-quality brands think they are smart and leave out the two $0.001 resistors needed for the device to advertise itself. This means it will only work with a USB-A to USB-C cable, and not a real USB-C charger.