I have a portable speaker thing but I've lost the charger.On the unit itself it says "15v DC".
I know this might sound like a silly question but what kind of charger do I need.The unit has a built in battery and I plugged a 12v charger into it but although I could play the unit it wasn't actually charging the speaker system.
Please help

One that outputs 15v DC

The voltage is the important thing. Get one that does exactly the correct voltage. After that you are interested in current. This doesn't have to be so precise. Check your instructions. If the supplied adapter was say 3.42 Amps then anything that and over will be fine. The device will draw the current it needs. So as long as the power supply can deliver at least enough then anything over simply isn't used.