They dont have seperate power supplies, The only amplifiers that really have seperate power supplies are mono blocks or a dual mono type design. What you're probably thinking of is something like "discrete power output" or something along those lines, which is basically just marketing jargon for "crap you havent the slightest clue about what it actually means but ours says it and brand x doesnt"
When in comes to power supplies in an amplifier, you really only start to see good ones in higher end equipment. Because they cost money. And when you start to get into the higher price bracket stuff in many cases (not all) it becomes less about "how cheap can we build this thing and still have it work" and more about "what can we do to make this as good as it can be?"
In nearly all, if not all recievers there is only one power supply.
