Addition from Richard Hoskins' great comment below:
Worst case failure could be that the AC adapter catches fire. When it comes to power delivery, it is best to be conservative and not exceed manufacturer's specifications.
By using the AC adapter which can output lower current than the one supplied with the laptop, you are running the risk of your laptop pulling more current than the AC adapter can handle. If that does happen, likely failure would be:
- The AC adapter would quit working by tripping over-current protection
- With the high current causing the temperature to rise, the AC adapter could physically break.
With that said, you are likely OK especially if the temperature of the AC adapter isn't hotter than the original. I just wouldn't leave it plugged in over a long weekend running software that pulls maximum power. If you do plan to do so, test doing it under supervision first. :-)
It depends upon what the input requirement is for your laptop and the specs of the AC adapter. From the specs given, you may be at risk of the second (smaller) cable failing. Does the smaller cable get warm at all?