What's the correct plug for 20Amp power cord?

A "20 amp" plug won't give you more power than a 15 amp one. The power drawn depends on the load (your amp). A draw of 20 amps would mean 2300 watts. If your amp were only 50 percent efficient it would be putting out more than 1100 watts...continuously! Your equipment can't draw enough power to overheat a 15 amp plug.

Audiophiles like to use oversized wire so as to minimize voltage drop. The fact that such wire could carry high current (which is why most people use large wire) is irrelevant.

Per UL/CSA if the power cord is rated 20-Amp, it must have a 20-Amp wall plug. Also 12 AWG wire. I would contact JPS to see if it indeed has 12 AWG wire.

There are NEMA-style plugs, connectors, and receptacles configurations on pages 696 - 701 of the McMaster-Carr catalog:

http://www.mcmaster.com/

Regards
Rich

Nema 5-20

What determines 20 amp is the wire from the box to the outlet.i.e. 20amp requires 12 ga. wire/ 15amp is 14 ga. Be sure the value for the breaker controling that outlet is 20 amps. Plug a radio in that outlet,have it playing. Then go to the pannel. Shut of the 20amp breakers one by one. If your radio shuts off---that's the breaker. There are different 20amp connectors; just so the breaker that turns off your radio, says 20 on it. In our building, the kitchen GFIs are on a 20amp circuit / but accept standard plug prongs. (Perhaps in your kit. the same is true.)