It means, don't worry about it. He is probably using the least expensive transformer he can get and the latest one is 9VAC. Some of mine from 1995 had a true large white wall wart. The later ones have a transformer with wire from both ends.

Anyway, by the time the AC gets rectified inside the A4, the resultant DC is 1.4 times the AC input. The input to the A4 is a full wave bridge rectifier and that allows the input to be AC or DC of either polarity, a good design.

Nominal line voltage is supposed to be 117 VAC, however mine is always on the high side and is about 125 VAC. This too will affect the output of the transformer.

I wouldn't hesitate to use either xmfr on either A4.

I have number 10 A4 on the way.