Electrical Question - dumb one - but a good one

What is the input AC power consumption of the Amp?
Volt amps, watts, or amperes?
A 120V 15 receptacle by code can handle 1440 watts continuously. Continuous by code is three or more hours.

The power amp manufacture may have installed the 20 amp IEC because it holds the female IEC connector better in place than the 15 amp IEC connector, not because of how much current the amp draws.

You can buy UL listed power cords with a 20 IEC connector and a 15 amp plug on the other end.

Also, judging by the wording of your question it's possible that the existing receptacle is already a 20A receptacle. 15A plugs can be plugged into 20A receptacles, but 20A plugs physically cannot be plugged into 15A receptacles.

A modern 20A receptacle looks like this. A 15A receptacle does not have the horizontal t-slot.

Re retrofitting the existing cord, obviously you have to make sure that the gauge of the cord is adequate to support the current drawn by the new amp. And if the gauge is not adequate to handle whatever the code requirement is for cords that have 20A connectors, it's probably not a good idea to use it because it might be used in a wrong application in the future.

Regards,
-- Al

The current rating is based on overheating if the specified current is carried continuously. A 15 amp rated plug will handle any current surge that your amp will demand just as well as a 20 amp plug.

no, your 3-prong plug is fine, you just need to change out the bit at the component.

you can also get adapters that will convert a 15 amp to a 20 amp if you want to try out the cord before you mod it, i've found that using good adapters on power cords doesn't do much negative...

good luck!