Yamaha USB charger thingy

[sigtrm]

Mines showing AC charging, I already checked that.
I was also looking for an app that shows the exact charging current (rather than adding an ampermeter inline), in order to compare to other chargers, but didn't find any that I liked.

Can you recommend such an app?

AFAIK there is no good way doing that programmatically. Just get some cable lying around cut it and measure with proper men tool;-)
Even if your phone shows AC you can test if shortening data pins helps with charging. You can check two things destroying one cable;-)))