Power cord can add a certain coloration to the final sound (think the power cord as a RC..RC..RC network). The coloration is usually not huge, but if your amp have a certain coloration you don't like, changing to a different power cord could mask the un-desired signature of amp/source.
For example: to fix the Stax T1S/W's coloration in human voice, one can try a pure silver/teflon power cord. That might take the voice abbrasivness away. However doing so might lose some (perceived) hyper details.
Dynamic phone/amp are usually not that transparent anyway, different power cords might not make much a difference in your set-up.
Save your power cord money, go electrostatics.
