You can, but in general the final result deteriorates a bit. Also your exposures need to be longer or more of them.
Difference is that a barlow is basically an achromatic negative lens and so makes the image bigger by diverging it.
I assume that a powermate operates more as 2 achromatic lens where the first is positioned such that its focal plane is coincident with the prime image and so the output is collimated. This feeds into the second and that would have a focal length of 2x the first. Then the formed image is again 2x in size. Optically the scope it is used on should not matter either.
I assume the Powermate design is better, also the expansion is fixed at 2x (or whatever). Will be longer, and I expect by a reasonable amount.
Better warn you this is guess work as I have never pulled one apart, nor looked for the optical configuration but that is what I half expect.
One ignored aspect of a barlow is most are sort of generic and not for a specific scope. So don't expect match optics.