AC Adapter tolerance

[crobicha-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org (Chris Robichaud)]

I have a Motorola WR850G wireless router that I cannot find the AC adapter
for. The back lists the input power as 12 V DC, 0.5 A. I only have a basic
understanding of volts and amps but is it true that using the wrong adapter
may damage the router? If I give it more volts or amps than is recommended,
am I risking a fire? How much of a tolerance do these things usually have?