First off, USB is a standard, the exact voltage and current may vary slightly from device to device as long as they are in the range of standard's specification.
So the question about using the stock "charger" is irrelevant. All wall chargers must put out voltage and current in the same range as the standard's spec. And the charger is irrelevant to those of us who connect to our PCs/Laptops where again, the voltage and current may vary slightly from device to device.
With all that said, I have the scroll jitter issue also. When connected to my laptop via USB, in portrait mode, my scroll lists jitter on any VERTICAL scroll. If I'm in a browser, I get vertical jitter when scrolling vertically, but no horizontal scroll jitter. Most list menus are vertical in portrait mode so they also jitter.
If I turn the device to landscape mode, ALL jitter goes away, horizontal and vertical. This seems to point to some SOFTWARE issue because if it weren't, you'd still get jitter in 1 axis since vertical just becomes horizontal in landscape mode and vice versa.
Also, if I unplug the device from USB, all jitter goes away in either mode, landscape or portrait.
To duplicate, while plugged in to a USB device or charger, go to a web page in the browser, put a finger down and scroll a bit vertically then stop keeping your finger down. I get varying amounts of vertical jitter. I can do the same on a home screen page by holding my finger down on an icon or widget as if I want to move it, move it slightly vertically and then hold... it starts to jitter vertically.
Very annoying. Hopefully this can be fixed a software update.