ABout all you can do is call them and ask about their own label powder. I suspect its Goex powder that does not meet Goex standards. This, because they are a distributor for the Goex powder, and are located near the factory.
Years ago, when the factory at Moosic, PA was having trouble with quality control, I acquired a few cans of Goex that were, frankly, terrible. Lots of fines in the powder. Someone at the factory thought they could mix different granules to come up with the same PRESSURE loads and it would not make a difference. In cannons, it probably doesn't. But they didn't think about how it was that we could keep that powder " mixed " in our cans or horns so that we did get an even mix, instead of only load of coarse powder, followed by a load of very fine powder. It was so bad you could actually hear the difference between like powder charges.
As has been suggested, I would be thinking in terms of using the really cheap powder for blanks for re-enactments, and parades, rather than using it with PRB or conicals to shoot them. Since I have already learned that screening powders to check on their consistent size of granules produces more consistent charges, and resulting velocities, I would be inclined to screen the cheaper powder to see what I had. And, this would be a very serious topic of discussion with the people at Jack's.