Just to be clear the power that's limited is the power input, not the suction power.
Previously they were selling vacs based on the power input wattage ie how noisy and hot do they get, rather than on how good they are at suction. This meant that manufacturers completed to produce terrible heavy wasteful vacuums.
Now there is that standard label with the a to f rating for cleaning efficiency, they can complete on the thing people actually want. A bit like what they did with led light bulbs, you used to choose the wattage now you choose the lumens.
The"equivalent to 1600w" thing is probably like the fact they label led light bulbs in equivalent Watts, just so you can find what you wanted.
Hope that is helpful!