20 amp power cords vs 15 amp power cords

As far as the ampacity difference between a 15 amp plug an a 20 amp plug there is no difference. Blade size and thickness are the same.

Blade configuration is different.... A 15 amp plug will fit into a 15 amp or 20 amp receptacle.

A 20 amp plug will only fit into a 20 amp receptacle.

A 20 amp receptacle can only, by NEC code, be connected to a 20 amp branch circuit.

Two or more 15 amp receptacles, (a duplex being two), can be connected to a 20 amp branch circuit.

Maximum continuous FLA amps safety standards for a NEMA 5-15P plug is 12 amps. So if the FLA of a manufactured appliance is 12 amps or less he can use a 15 amp plug.

Most convenience outlet branch circuits in homes are 15 amp with 15 amp duplex receptacles.

One reason the biggest consumer home portable vacuum cleaner only comes with a maximum 12 amp motor......

Also the reason pretty much all power amps have a 15 amp AC power plug.

A lot of aftermarket power cords use at least the equivalent wire gauge wire size of #12 awg. Ampacity rating for # 12 awg wire is 20 amps.

Maximum NEMA continuous FLA amps safety standards for a NEMA 5-20P plug is 16 amps.

The weakest link in the power delivery chain to the power amp is the IEC connectors IMO.....
Not the NEMA plug.

If your 20 amp lineis protected by a 20 amp breaker then I would use a 20 amp rated power chord. If the breaker is only 15 amp then the 15 amp chord will be ok. Also remember if the amp is the only thing on the circuit you are probably only drawing 4 or 5 amps so either chord will be ok