What kind of power supply can I use to power the unit when it's indoors? I have the original one, which works great, but there are a few other locations where I'd like to have alternate power supplies already set up.

I have a flatbed scanner whose 13.5-volt power supply works perfectly on the Empeg.

I also have a 15-volt, 800ma power supply for a pair of multimedia speakers that looks like it should work great, but since its voltage is that much higher, I'm afraid to plug it in without asking first.

What guidelines should I use in deciding whether a power supply is OK for the Empeg?