The picture shows USB micro, not USB "C". This model battery comes in a USB "C" model as well as this one. I have both and the USB "C" model powers the mix pre with no issues.
Yes, that was my mistake. The one he has does have USB-c out.
10% of the people on Amazon rate the battery as a 1 out of 5, however, and there is this question:
Question: Why wont it charge from the usb type c as output, its only working as input
Answer: Not enough information to answer the question depends on what you're trying to charge unit could be too small to charge this item or other factors could be part of the problem
By Robert Helms on April 2, 2017
I have come to find out that the power bank unit can't recharge through USB C. It will only recharge through Micro USB. It will give you a double 00 if you try to recharge your bank through USB C .
By The Amazonian on August 11, 2017
Mine has this same issue. I'm trying to charge a Nexus 5x from the USB-C output but it's not working. It only works as an input.
By JTompkins on April 30, 2017
Actually, I just tried something out. I saw that my phone was charging the battery pack so i just rotated the usb connector 180 on my phone and plugged in and then it started to charge the phone. That's weird! Who the heck would want to charge a 20000mah battery using a phone??? Dumb! But it works now, at least.
By JTompkins on April 30, 2017
I admit the question and some of the answers are confusing, but I wonder if there are quality issues such that some people experience issues trying to use the USB-c for output