Power command is nothing but a full shift transmission where we are in control of gears speed and can be adjusted by pushing up downshift buttons. May be this helps.
We have what I think you are referring to as
power command in our JD7420. It is an electronic shift up or down by push button on the shift lever. The shift lever has 4 gear positions A<B<C<D and we shift with the lever to get in them . On top of that lever is 1,2,3,4 positions, and that is push button. It is nice because you can do it all quickly and it will downshift automatically from say 4 to 3 if you are going too slow for that gear.
Our JD7210 has 2 sticks and shift each one separately and manually. .. Bordercollie