Calciphylaxis. Calciphylaxis is a condition characterised by necrosis (cellular death) of the skin and fatty tissue. It is seen mainly in patients with end stage kidney disease. It is also sometimes called calcific uraemic arteriolopathy.
Besides a data link, USB provides 5 +/- 0.25 volts to power an otherwise unpowered device or charge a battery in a self powered device. A USB controller or hub is required to power one unit load (100 mA, a low power load). It can optionally power up to 5 unit loads (500 mA, a high power load).
Your device is USB 2.0 and the max load a USB 2.0 port allows is 500ma. You have stated your device can draw up to 850ma. The load your device puts on a single USB port exceeds the maximum allowed power consumption written out in the USB specs. A Y cable is a hack way around what the USB specification allows.