When I upgraded to a Rosetta and a Pi3, I bought a batch of JuiceBitz cables to try out various installation ideas.
The one I preferred in the end used a shorter 0.5m cable, but with that I have been plagued with 0x50005 issues and more recently, Wifi Losses.
I flew today and it happened again just after landing. Having time to investigate, I noticed that the Micro Usb plug was warm. Pulling the plug and touching it, it was hot!
Getting back home I tried another longer JuiceBitz cable and no such issues and the Throttled value went away.
Close examination of the suspect plug and the socket in the Pi revealed no issues so I decided to dissect, carefully removing hot melt glue from underneath the casing. The first image reveals all!
You can see a thread of braid is loose and able to touch the end of the green wire's connection, The green wire is data I beleive but is possibly also connected with a sensing circuit, usually a resistor. When I connect the USB-A of the cable into the power pack and touch this loose wire to the Grreen wire, the power pack activates so it senses a load.
Moving the loose wire away and plugging the lead into the Rosetta, the plug still gets hot and the device throttles. This, I beleive, to be due to poor soldering of the too short Red wire where solder is used as a bridge.
Hopefully a one off but it shows a bit of a quality control issue even with these cables! So, even if you are using a good power pack and a (clearly good spec) JuiceBitz cable and still experiencing power issues I suggest you try another cable as a first resort.
***Edited to add 3rd Pic, the main culprit, really bad (dry) soldering on the +ve lead which is where the heat is emanating from!
Vic