If I'm understanding you correctly and it uses an external transformer, then I imagine sending twice the current can't be helping either.
Actually, that might be the only thing saving him! Power is calculated in watts, and watts are voltage times current. The original power adapter is supplying (9 * 0.6) 5.4 watts of power, and the other one is supplying (5 * 1.2) 6 watts.
From what I remember the amps should only cause a concern if there is a failure in the transformer that results in more amps being drawn than normal. In this case I was daydreaming when I read about the voltage and at the same time I'm just overly cautious. My electronics studies are from the distant past, so my brain is a little fuzzy.