Shielding only works if the shield is connected to ground. You need to make sure the power cord is grounded, and then connect the shield at the female IEC end. Or even if the power cord is ungrounded make sure the shield is only connected at IEC end to avoid ground noise being induced into the lines from the wall.
Better option: don't ground your power cables. Build a grounding device and attach a wire from the chassis screws on your gear to a binding post on the grounding device. It would function as a star ground for your whole system and only a single grounding point. No more ground loops either. That's more work obviously. And all power cords should be grounded otherwise.
Better option: don't ground your power cables. Build a grounding device and attach a wire from the chassis screws on your gear to a binding post on the grounding device. It would function as a star ground for your whole system and only a single grounding point. No more ground loops either. That's more work obviously. And all power cords should be grounded otherwise.