The power cords are just there to energise the panels and then keep them energised. Not much current flow, and I suspect it won't even matter if the electricity they use is 'dirty'.
I've never bought into these 'expensive powercord' theories, they all sound hocus/pocus to me.
If anyone can tell the difference in a blind test, I'll convert in a millisecond
I do believe in mains filtering though, especially if you share electricity with workshops or industrial estates. There are some capacitor-based gizmos that you plug in the mains and they claim to clean it, I've got one from the canadian UHF site - maybe it works, who knows, at least it was cheap.
I also have a couple of 'filtering' mains cords from Russ Collins, Yello or something. I can't hear any difference even when they are on source equipment, but I use them anyway since I've bought them (just in case
)
I've tried one on an SL3 and tried hard to hear any difference. Nothing.
Maybe my mains is clearer than most (dedicated ring), maybe the whole concept is placebo:meditate: . It's your money.
As for cleaning the panels, if they are dirty, I'd go for it (can you see dusty circles on the mylar from up close?)
Be careful, some SL3 panels slide upwards, some downards.