For all of my sharpening, I use a sharpening compound. I either use Isomax 81033 Buffing Compound by easypower for stainless steel or FlexCut Gold or Zam. Zam is the hardest and by far the best for using on power strops. However, I have also use the Isomax on a power strop too. The Isomax is green waxy based material similar to the FlexCut Gold. These materials readily adhere to leather. The Zam can usually be purchased though carving vendors. The Isomax can be purchased at most good hardware stores. FlexCut Gold can be obtained through most carving supply houses.
Notes
If you want to use a power strop then I would recommend making one yourself. The artists guild in Pueblo Colorado, researched materials that would make good power strops. Ones that would stand up, hold compound, stay flat and true to shape and would be readily available. They ended up using MDF. MDF is Medium Density Fiberboard. It can be obtained at most all home supply stores including Lowes and Home Depot. Make a circular wheel from 5/8 thick MDF. Can do this by marking a circle on the MDF. Then drilling a pilot hole in a press at the center. Mounting on a carrier board with a screw or nail. Then, clamping the mounting board to a band saw and turning the MDF to cut the perfect circle with the band saw. Then drill out the pilot hole to the correct diameter to fit your mandrel. You can use your 3/8 inch drill to turn your strop. Then, you can mount the drill on any picnic table etc. with a quick clamp and power strop any ware. To make a mandrel for your wheel, use a long 3/8 inch bolt, and washers backed with sandpaper to provide friction to capture your MDF wheel. Place a lock washer and nut on the bolt, and tighten very tight. If you want, place another nut to lock the first down. Make sure you get a 3/8 bolt long enough to provide adequate extension of the bolt past the nuts. Chuck it up into your drill and your in business.