Hello,
Could you tell me if the USB input of the DS Jr is powered or not ? (= need the 5v from the cable to work)
I’d like to try an “high end” USB cable, but the price difference between powered and data only model is $100 (powered is more expensive…), so if I can save some money with the data model, it would be nice…
The need for power via the USB is a function of what you’re plugging into. Only small passive devices like signal converters may derive power via USB. As DSJ plugs into the AC powered wall receptacle it receives no power from the USB port. Only data is used from any of the digital inputs on the DSJ.
Ok, so a data only usb cable should work 
Not necessarily, some systems need to sense power in the usb cable. Some don’t. Ted Smith mentioned this somewhere.
To my knowledge (paging @tedsmith to verify), the DSJ and DSD use the 5V to determine that the connection between USB device and DAC has been established. I know our service team strongly encourages the use of certified USB cable - certified USB cables will have that little data trident symbol on them.
If my memory serves, a data only cable will sometimes work, though I’ve heard of folks have drop outs using a data only cable.
As Schroedster mentioned things aren’t quite that simple. The VBUS line on a USB connection serves multiple purposes, the obvious one being providing (optional) 5V power to a USB device. The non-obvious use is signaling when a hub or a device is added or removed from the USB tree. If you are lucky you can get away with not having the VBUS connected - but tomorrow you may not be lucky - it depends on the cable, the versions of software in all of the USB units from the computer to the DS… If you want to experiment you won’t hurt anything, but if something goes wrong try a certified USB cable before calling support, etc.
Amazon Basics cable worked from my laptop when I had to make-do with something longer.
Note: 2.0 USB seems to be more reliable with a variety of gear/equipment vs. the SS/3.0 output from the computer.