Hi hgtan,
Thank you so much for your ingenious idea!
Yesterday, just one minute before I was about to return this humming and pulsating device, I took heart and assembled an adapter just as you suggested in your post. As a power supply, I used an old 5V USB-Hub power adaptor.
Now the noisefloor is totally acceptable!
It would be great, if an adaptor like this could be bought, but I think it’s to special…
Again, thanks a lot!!!
Oliver