[AR Powered Partner 570 power supply]

I'd recommend using a 120 volt AC  for optimum performance.  The 14 Volt input is primarily for mobile use and specifications are not guaranteed due to dependence on quality of power supply.  ie fully regulated supplies work better than unregulated, but switching regulated supplies might introduce noise problems.

[AR Powered Partner 570 power supply]

Acoustic Research sold a power supply for these speakers. It was model # AV42 with specifications 13.5 volts and 1.7 amps center positive.  You could probably use any 12 to 15 volt adapter as long as it was rated at least 1.5 amps.