This worked great to power a Powered 10" loudspeaker. Hooked it up to the tractor battery to use on our farm for a small PA system (Mic and powered speaker) for our Open house day. I'm sure it would power a small audio mixer plus the amped speaker as long as you weren't pushing too much low frequency with a band or loud DJ music for extended periods. Hard to tell if the individual outlet power is 400 watts, or the combined output of all the outlets is 400w. I suspect the latter, but in my case, it was enough regardless.