|All Power supplies have a label on them that give the input Voltage and amps as well as the output voltage and Amps.|
The Input will be 110/230 Volts 60/50 Hz AC.
The Output will be 14 V 3.5 Amps for example.
You need to match the output with the input requirements of the device you are connecting to.
Volts should be as close to the input as possible. A little under is acceptable but never over.
Amps should be the same or more but never less.
If the device consuming the power is demanding more than the power supply is capable of supplying then there will too many Amps flowing in the circuit and things started getting over heated and burn out.
Volts and Amps are closely related along with resistance. To understand this relationship between Amps (I), Volts (V), Resistance (R) and Power (W) you need to study Ohm's Law. It is not complicated and bring it all into perspective.