Another answer is to get one of the chargers with adjustable voltage and a selection of tips.
The one I have has a slide switch for voltage, a mess of tips all on the end of the wire and a polarity switch. The other one has a rotary switch for voltage and a collection of tips in a small attached case. The tips attach to the wire by plugging into a little plug on the wire. Which way you put them into the plug decides the polarity.
I bought them a few years ago from an electronics or hardware store but don't remember which one.
The two I have get used for almost everything that needs to be plugged in except for computer gear.

Computer peripherals (modems, printers, external drives, etc) seem to be more fussy about how clean and steady their power supply adapters are. Often they are regulated power supplies with filtering to eliminate any current ripple or stray electronic frequencies. However since they seldom get unplugged or moved much the supplies tend to stay with the equipment more.

My answer to tagging wires is good old masking tape. If you peel a strip of tape off, lay the wire across it at about the middle of the tape then stick the two halves of the tape together it makes a nice easy tag to write on. It seems to last pretty well too.