Do power supply units/cables make a difference in sound quality?

Steve, Thank you for taking the time to post such an informative description on the subject of cables.  I buy into the contribution of high quality connecting cables between components up to a point of cost/benefit.  The value of a power supply unit costing 4 figures is questionable for me, given the stability and lack of interfering noise on my rural electric supply.  I am really curious about Lordmelton's suggestion to try HiFi Tuning gold plated silver fuses, I assume on my Threshold amp.  I wil explore that.  Thanks all.

Lots of smart folks offering opinions. I'm in the same throes debating whether to add something other than the Furman ELITE15 PF i Linear Filtering AC Power Conditioner that I own. Before I dive into a more expensive component, I'm having a dedicated line installed from my main panel to my stereo system. I also purchased a "Silver Cryo Receptacle" so the cost will be a few hundred dollars. I've talked with a few audiophiles that confirm, it is an inexpensive step to do before shelling out thousands for a power plant, conditioner, etc. that may/may not help. 

“I am quite happy with the sound from all sources”

^Your answer^

I wouldn’t buy the cables. 

As you can see, some say yes and some say no. The only way you can come to any conclusion is to try it yourself. Personally I found that some power conditioners can adversely effect SQ and that spending big bucks on power cable is a waste of money. There are many cables around $100 that will do the job admirably.

Indeed. That is my conclusion.  I will invest in a new cartridge for my turntable.  I think the Koetsu has worn down.  That will make a hearable difference playing records. Thanks all who took the time and trouble to answer my question.