It seems waaaayyyyy to hard for the industry to have a standard size and polarity for these things. 
We can send rockets into space and have boosters self land but a standard power adapter....apparently not! 
It is human nature to ask such questions, but life is not quite that simple. Wall warts come in many voltages and configurations. Sometimes even the correct voltage and connector doesn't work properly (if too cheap to work right). I have a cheap surround decoder running from a 5V wall wart. It refused to boot-up cold, but would start if I unplugged and replugged the wall wart power jack at the unit (WW already stabilized).
I bought a replacement WW and unit now boots up...
At Peavey I used truckloads of WW back in the 90's before the customers pushed back against them hard (customer is always right). I used an AC WW so there was no polarity concern, but line cords mean never having to say "Oops I forgot the WW".
JR
