I swear to god I think charging w/ my USB charger SOMEHOW gave me my weird jittery stylus bug from a while ago. To recap, everything worked fine while it was charging (even w/ the usb charger,) but when it was running on battery with the brightness on max, dragging the stylus across the screen gave jittery results (so obviously some kind of power issue.) I sent the 3DS XL in to Nintendo for repair, and when I got it back, it was fine; till I charged it with the usb charger, and the problem returned. Since then, I started charging w/ regular charger and all of the sudden the problem vanished. What the fuck.
None of these issues occurred using the same USB charger on a regular old 3DS. Only my XL.