Those symbols are used for radio power. The real power is RMS (Root Mean Square), while PMPO means music power (Peak Music Power Output). How to compare those – you need to split PMPO by 3 and then you will get RMS (almost! not exacltly ). For example if you have JVC with 19W RMS / 50W PMPO.
RMS is a voltage that is putting to the speaker in Constance way, without worry of sound quality or speakers damage. PMPO is the highest power at the highest voltage, at the speaker that least less than second.
PMPO is a marketing symbol, because it’s much nicer for producers to put some big numbers. So to be honest, PMPO was created for cheating people at the shops.
When we speak about amplifiers, it is power that amplifier can produce at all time, without any damage.
There is also some compare with voltages. If effective value is 220V, and 310 is maximum (311V)it is because maximum value = effective * the square root. You can very easily check that by testing current by multimeter and than check at the oscilloscope. You will see that measure instrument will show 220 while amplitude of current at oscilloscope is 310.
How we can use that in practice way. In general, speakers power we split by 2 (or3) and we got amplifier, for example: if we hve 100 watts speaker, we can plug it to amplifier with power output abou 50watts. Of course we can plug stronger speakers but not too strong –obviously you want plug a subwoofer to headphones slot.