Power cords do make a difference. I even found that the power cord that serves the bias supply on my ESL speakers can make an audible difference. But the good news, IMO, is that cost is not a major factor. Cheap PCs can sound great. Expensive PCs can sound worse than factory-supplied PCs. I found that good speaker wire, if the gauge is high enough, usually make excellent PCs. Gauge is a major factor. Use 12-gauge from Home Depot or Loew's, if all else fails or on a budget, and if you know how to DIY a little. My theory, based on limited experimentation is that shielding and wire gauge are the major factors that distinguish good from bad, plus the amount of RFI and EMI in your own listening environment.