"R D S" wrote in message
...
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?

Unlikely to be a problem but its possible that a badly
designed exercise bike might have a problem with it.

And if not when is it likely to become one?

Again, impossible to say. It depends on what
the internal voltage regulator has heatsink wise.

And why do similar rated ones differ so much in bulk?

The ones with iron cored transformers are much
bigger than modern switch mode wall warts.

Is this just a build quality issue?

Nope.