Hi, I don't understand the question really, but a bit of info anyway.
Some amps, speakers and hi fi music systems quote their output in "Music Power", the highest output available some of the time, just maximum peaks here and there. Others will refer to the true output which is quoted as the "RMS" power output, this is what the amplifier or speakers will handle continuously.
I'm can't remember the correct relationship between the two, maybe someone can chime in, but if one sees speakers with a 150w music power rating, its true power handling [RMS] is a lot lower than that.
For what it's worth. Taff
PMPO is the total peak power of all the channels in an amp added together. it is also calculated from max negative to max positive swing if a pure sinewave was put into the amp. RMS or root mean square is the positive half of the sine wave divided by the square root of 2 ie 1.414
for example a LM386 run from a 9V battery usually gets around a 4v swing positive and negative. so the Vrms is 4/1.414 or about 2.9V , 2.9V into a 8ohm speaker gives a max current of 0.36A, W=VA so wattage output is 2.9 x 0.36 = 1 .04W RMS output power.... PMPO on this single channel example would be 8Vx0.36A = 2.88 W PMPO almost 3 times bigger in this example.
sorry for the math and the lecture.
Limited info, but I suspect it is using the lowest and the highest of the DC supply voltage range recommended for the circuit and giving the watts produced at these two levels so you have an idea of what you will get from the circuit.
two things can determine the output power of an amp circuit. first is the voltage powering it. some of the ebay amps can say 12v to 24v . so with a higher power input you will get more out. but 24v will not be 2x the power output of running the amp at 12v.
the second thing that is more usual is that they will give you a different power output depending on the speaker load. like either a 8 ohm or a 4 ohm speaker.
usually the circuit will tell you what it expects as power and load. most of the cheap ebay amps are amp on chip designs like LM1875 etc... http://www.ti.com/lit/ds/symlink/lm1875.pdf
most of the ebay amps are direct copies of the test/suggested circuits from the data sheets.
pluss to confuse people more what Taffy said. some adds inflate the power output by using PMPO peak music power output. but Hi FI amps etc usually quote RMS power ( root mean square) .
tl;dr version... use a 12v battery instead of a 9v and you will get more power. use a 4ohm instead of a 8 ohm you get more power. but only if the amp was designed for it.
Some amps have an attenuation of output.
Example: Like a 50 watt amp that has settings to lessen that output for smaller venues or home studio/room use will have settings for 30watt - 15watt - 7watt - 5watt - 1watt or .5watt for whatever setting you want.