What is the name of the tool?


Forgive my absence of knowledge, but what is the name of the tool that one uses to measure the wattage coming out of ones speakers. I called it a watt meter to my family and got something that measures the watts and current coming from the outlet to the powered device I was using instead, for Christmas.  
rickytickytwo
Back in the day, Technics made a SH-9020 Power Meter.  I not only sold them, but personally used one for quite awhile.  Pretty accurate if I remember correctly.

https://www.kenrockwell.com/audio/technics/sh-9020.htm
The Illuminated Power Output Watt Meter on the MC501 is peak responding, and indicates the true power output of the amplifier
No, they measure voltage. Power would only be correct for a pure resistance. Examine loudspeaker impedance curves. Some of the more egregious ones have a 10:1 impedance ratio.
I'm curious as to why this is relevant. Obviously you are trying to measure this for a reason. Can you explain?