Like petrol in a car, electricity is the 'juice' that makes your system work. And, like petrol, if that 'juice' is dirty or polluted, things don't work as well as they should... no matter how good the system.
This is why it's vitally important to get your power supply sorted first, before you improve anything else. If you start with your interconnects and speaker cables you could be making things worse because higher quality cables will be able to reveal any problems 'downstream'. Get the power right, though, and better cables 'upstream' will only bring benefits.
The Hi-Fi Establishment was, for many years, quite dismissive of the importance of clean power on sound quality. The attitude had been that as long as you connect 230 volts to your system, the sound quality you get depends on the quality of the equipment itself.
The truth is that poor mains quality ruins the sound of even the best equipment. In fact, the better the equipment the bigger the difference. On the other hand, even the most modest system benefits enormously from good mains.
An example of the importance of mains quality to sound quality is the effect that a high quality mains cable can have on even lowly portable stereos. If you can hear that on the lowest of the low in Hi-Fi terms (and in our experience, you can) then just think how much bigger the difference will be on better equipment.
The quality of your mains power is absolutely fundamental to the reproduction of music. We say ‘fundamental’ because the power is the source of all the sounds from a system and the quality of the sound depends directly upon the quality of the power.