I just noticed this recently with a USB-C flashlight. It wouldn't charge with a C-C cable but started working when I switched to an A-C cable. Good to know why.
Wow...I was just about to throw out a charger that has both USB-A and USB-C ports. The A ports work to charge a device I plugged in, the C ports do not. I thought it was the charger, I'll have to check some more.