Quality of Power

[Confused]

I often wonder how much of the perceived influence of the sound due to variations in the mains is perhaps more a case of variations in what is being listened to and the listeners mood at the time of listening. I do sometimes think my system sounds better on a Sunday morning, but maybe I just tend to be in a more relaxed mood on a Sunday morning? (As it happens, I do tend to be in a far more relaxed mood on Sunday mornings!)

So here is a question, is there a practical way to actually measure the quality of your mains? I suspect the quality of the mains is probably relatively good where happen to live, so I would like some way to actually test this before rushing out to spend lots of cash on a mains conditioner or similar.