
It may charge, but not power your device. If there is sufficient power, it will charge, albeit slowly. The power delivery spec allows for power negotiation. Vice versa, if there is a Quick Charge 2.0 or 3.0 USB-C charger from other devices nearby, can it be used to charge the Macbook 12 inch? (MagSafe power adapters have a chip built into it to prevent using an underpowered charger).



Since it technically doesn't have enough, it will either charge slowly or not at all.

Yes, it can be used and you will not cause any damage. If there is only the MacBook 12 inch USB-C charger nearby, can it be used to charge other USB-C devices, such as any Android phones that also use USB-C? (will it be "too powerful" and damage other devices?) This answer is indented to be canonical answer for similar questions and applies to all devices that utilize USB (Type A or C) chargers and conform to the USB Power Delivery specification (version 2.x through 3.x).
