What happens if I use lower amperage in "input"?

Solution 1:

As long as the amps meets the device's minimum required to run, then lower amps generally shouldn't cause a major problem. For a laptop charger I could see it not having enough power to actually charge the battery, but still running OK or maybe slowly draining the battery (as if it weren't plugged into a charger).

If the amps were too low (and there were no battery) then the device probably won't turn on, or might try turning on & fail repeatedly.

But you let the magic smoke out - it won't work anymore :( If you took apart your laptop you'll probably find a burnt or blackened part that has failed or exploded. Capacitors can explode... but could've damaged other less obvious parts too.

You might still be able to test the power adapter (if it still works) with a multimeter and see how many volts it's outputting and if the polarity is right. Using a small test light / light bulb as a small load might help - I saw a power adapter ("wall wart") once that would output 20V with no load, but when plugged in it read 14V, but it seemed bad & was replaced anyway.