Polarity specific wall warts - or not

[mrbigstuff]

I busted a wall wart (stepped on and broke the prongs right off) that is made for a 7.4v nimh battery of mine. Upon opening to solder a new plug, I was wondering about the polarity and whether it matters if I solder in a polarized plug where the original had none.

[btfc]

Given that the old one could be inserted either way, no, you’ll be fine.

[Filliam H. Muffman]

There is a chance that the device has an internal ground. For power supplies with barrel plug, occasionally the outside of the plug to the device is grounded (more likely to be three prong). Make sure you do not have 120 V to the outside of the plug. Verify it with a multimeter after you think you are done. This is the main fault in most counterfeit iPhone/iPod chargers that have electrocuted people, not being properly isolated between primary and secondary.