If you're a new DJ thats a bit strapped for cash (or one that likes a bargain) you will probably seen the cheap amplifiers on Ebay, usually advertised by two german companies by the names of = etc-shopde and electronik-star-de. They are german companies that sell alot of DJ equipment on here and by enlarge they seem decent companies. The reason why im writing this is because their amplifiers and speakers are somewhat deviously marketed as with regards to their power outputs. Now as DJs im sure youll agree that we need accurate and correct power ratings for stuff we buy, the pointless and untested "PMPO" and "MAX" power ratings are totally useless and do not give you any clear idea of how much power a piece of equipment has to give, for example, a cheap £9.99 kids Radio/Cassette player can be advertised as having 180 watts PMPO or MAX, contrast this with a reputable brands output figs for a similar unit, rated at 5 watts RMS (Root Mean Square)!!!
Now these companies advertise their products using the PMPO system of power measurment which can be misleading, you'd think 1600watts PMPO and 512watt RMS was enough to power a decent set of 15" cabs, until you read the instructions which say that they are infact only 100 watt per channel RMS, barely enough really to power anything to be honest. Why this discrepancy in the figs? well, heres the truth:-
Whilst rating Amplifier output there is only one way to correctly measure sound power output is to measure it in Average power output, otherwise known as RMS (Root Mean Square). No one knows the correct origin of the PMPO (peak measured power output) or Max reading but it is usually accepted as the max amount of power an amp can give before it literally blows up, even if it takes a millisecond to blow, they use that measurement!!! No this crazy measurement can hardly be used as a useable guide to how much power is available. Now the Average power rating or RMS rating is far more accurate, this is a rating that tests the units average (over a sustained test period) power output,and not the power it can take before it blows up!!!
Another thing to consider is the RMS ratings over a 4 or 8 Ohm load, now if you just running a regular set of speakers then you will almost certainly be running the amp with an 8ohm load, youll only get a 4ohm load with more than one set of speakers in series. Now sometimes companies who want to give their ratings in RMS but want to make them look more will use the 4ohm rating, this is always higher then the more realistic 8ohm rating (usually nearly double). This explains why my Amp was rated at 256watts RMS per channel (it was 4ohm) and not the more realistic 8 ohm load which is more like 100 watts per channel RMS.
Hope this was of help...