I have had laptops which ran at the same voltage but had different power requirements. 1 of the laptops shipped with a 60W power supply the other shipped with a 95W ps. You could indeed run the 90W laptop with the 60W ps BUT if you did for a extended time the 60W supply would first overheat then you let the smoke out. That is it will burn up.
This is why they label devices with the power draw. If you look at your collection of wall warts you will find some rated for 12V and 500ma, another will be 12V and 1500ma. You need to take care and match the voltage and power (current draw) with the device to be powered . You can use a device rated to draw 500ma with a power supply rated at 1500ma but not the other way round.
As above if you use a lower power rated power supply with a device which draws a higher current, it may work for a long time or it may not. You are taking a chance of burning up the PS.