I am trying to charge my 3DS without the original charger via USB cable (by stripping the wires). On the back of the 3DS, which metal contact is positive and which is negative?
When looking at the port like so:
The left hole is Negative and the right hole is positive. I also believe the pads are the same.
5V also shouldn't hurt it because the charging circuit inside the 3DS should prevent anything bad from happening. I see a lot of 3rd party chargers that are just straight through USB to charge-port.
Hope this helps!