power cord directionality

If you're not getting ground loop noise then it doesn't matter. The only reason for the arrow is if they lifed a shield on one end in an unbalanced wire. Yours is balanced with the three pin XLR the arrow is irrelevant.

Apparently the manufacturer honored the directionality of the wire (raw conductor) and the directionality of the shield. So, if the label is wrong the umbilical is in the wrong direction. If the cable can be reversed try it both ways to see which sounds better.

On some cables the ground wire is only connected on one terminated end. It helps to reduce ground noise or hum. On a power cable that is grounded or has a ground plug it should not matter that much as long as both ends are terminated and your equipment that is using the cable is utilizing the ground. If it not using the ground then we might run into some ground noise issues because the signal is still there. If your piece of equipment does not have a ground ( like on a receiver) then it can cause ground loop hum. In this case the wire is not terminated or only terminated on one end. Also I have heard if you have a very sensitive system then the way the copper is extruded determines the direction of the signal.