Power cables have zero influence on sound stage.
Power cables can inductively couple with other cables. This will cause noise from other cables EMI fields to be transferred to the power cable in question. Similarly, when inductive coupling takes place, the EMI field of the power cable in question is transferred to other cables.
Much of this inductive coupling can be mitigated by isolating (not bundling) power cables from other (power and signal carrying) cables.
When isolation is difficult or impossible, the use of ferrite beads can isolate the noise source. This is why switch mode power supplies have ferrite beads on their input and output cables.
Shielding, when done properly, can be effective. I say “properly” because most unbalanced audio cables use the shield as a signal-bearing conductor. This causes induced noise to be brought directly into the signal path. The correct way to shield an unbalanced audio cable is to add an additional layer of shielding which is isolated from the signal-bearing conductors, and tied to chassis ground at only one end (preferably the source side). Typically the most convenient place to ground the shield in audio systems is to the preamplifier chassis, as the preamplifier is the hub of the system.
Going back to the OP’s claim about loss of sound stage, that is due to other factors. Most likely speaker placement and phasing.
