I'm looking for the wall wart for an exercise bike in my bin of such
things.
It needs 9v 0.5A and i've found one that's 9.6v 0.6A which (accepting
there's no danger of ever finding the original) is closer than I
expected to get.
But I have a 12v 1A with a longer cable, past experience tells me there
will be no bother using that but is it a problem? And if not when is it
likely to become one?

And why do similar rated ones differ so much in bulk? Is this just a
build quality issue?