High current amplifiers will usually put the specifications of the maximum current output. The others will not. @erik_squires is correct the doubling is a good proxy.
My real interaction with this issue was in 1980, I bought a 200 watt/channel (?) 75 pound, highly regarded Yamaha amp… it was a complete whimp… I bought a 250 watt / challenge 125Pound Threshold s500 that completely and utterly blew away the Yamaha… the Yamaha sounded like a cheap transistor radio… in comparison to the Threshold. The Threshold had at least 10 times the current. Took hold of the speakers and told them it was in charge.