Q:

How to determine DC Amperes required for Amplifier?

I'm trying to understand if there's any relationship between the rated wattage (RMS) of an audio amplifier and the corresponding power requirements on its power supply.
Practically, if I buy an amplifier that does not have its own power supply, is there any formula or inference I can make to help me determine the minimum wattage of the (bench) power supply I should purchase?
To provide an example, consider the following cheap amplifier and a power supply such as this one. Is it powerful enough? Not powerful enough? How can I tell?

A:

your amplifier is capable of delivering 240 Watts of energy. 
Power (Watts) = Voltage (volts) x Current (amps)
Therefore the current range is:
Power/Voltage = Current

240 W / 12 V = 20 A
240 W / 26 V = 9 A

So when powering the amplifier from a higher voltage, you are likely to require less overall current.
Maximum current drain at maximum power is 20A
The amplifier board indicates 90% efficiency, so you may well need to factor this in:

(240/12)/0.9 = 22

So in order to deliver 240 Watts you may need to supply 22 Amps.
Looks like that PSU will probably be good enough to power that amplifier board.

