1st, the rated output on unbranded/fake amps is never what they claim to produce. so ur never getting the rated rms. also dont get too happy when u see the 2000/3500/5000watts on the amp. This is just to make the buyer think he has somthing out of this world. V all have that 1 friend who will tell u he has a better 4 channel amp then ur branded 4 channel (let alone mono), only to find out its a fake
2nd, the guts. ever seen the welds and joints, the material and design on the more expensive cars? why do you think only the chassis of some cars is more expensive then a whole car. the built quality, the components used, their lifetime etc are all top notch. same case with the amps. open 2 amps, look at the guts (the circuit boards and the components used) on both the branded and non-branded amps. ul get the idea
3rd, signal ratios, tuning, filters, Thd ratios, efficiency etc etc. branded amps will give u the best output for ur money without compromise.
i hope ur getting the picture.