When I found myself in the same situation, a power-supply from and old USB hard-disk helped out (12V, 2 Amp). Those are pretty common and also all that I’ve seen so far have the same polarity.
Not all power supplies are created equal. There are other specs other than voltage, amperage, and polarity that make for a good power supply such as noise filtering, radiated and conductive EMI, etc…
I’m sure (or I hope) that the MOD team tested for good audio quality and safe functionality.
Sure we did. We picked this power supply out of 3 other already filtered by our requirements. Despite the enclosure looks like any other generic power supply it’s a good quality one.