I bought, received and tested this very useful little device:
I connected it's input to a recently bought SilverCrest 10.000 mA powerbank, which was fully charged.
The output was connected to my Zoom G3Xn multi-effect-processor, that is normally powered by a 9V DC - 500 mA wall-charger (which means it will consume about 400 mA, the maximum that the 'Joyo' can deliver).
- The Zoom G3Xn became immediately active and was continuously used during 7 hours and 45 minutes, after which the SilverCrest powerbank was empty.
- Power dissipation was transformed into a hardly noticeable rise of temperature near the output section of the 'Joyo'-device, which is remarkable, since it had to deliver it's maximum all the time it was used.
- There was no measureable (noise) influence on the audio-signal: It was absolutely clean.
Conclusion: This is an excellent little devil, very useful on stage, and can be considered a gig-saver there!