Of course I could have misunderstood his post, but I think "it IS the Amperage that is important not the Voltage." is quite clear and is wrong.
In a simplified view wall warts are voltage sources with a current limit and non-linear source resistance. D.C or A.C. is important too.
I want to avoid somebody connecting a 12V 2A transformer as a USB PSU or even believing it could be done.
So how do you think that could happen, the bolded bit above??
What kinda connector, with a mini USB on one end, would one use??
I process to not knowing, but am prepared to be educated and informed.
I believe 5V is pretty standard for microelectronic devices, and current regulation is built into the device, generally.
Any charger for mobile devices will be rated 5V.
That's why USB ports are rated 5V +/- 0.25V.
The current/amperage is the difference....
and the load [device resistance]....
something showing 5V+ when measured will not have that voltage when a load is connected.
I think what flibblesan said, you misread, perhaps not misunderstood, but maybe both.