Getting warm is not really a great thing for a electrical cable. Are you sure it is original cord?
And can you define "very warm" that is not something good if it's as hot as I think your saying. Yes it could be the amount of watts of a S4 if cable is not right gauge. So check cable and see if it is original. And even if it is if getting "very warm" might be worth getting a new better gauge wire.
Thanks. It sounds like it is too hot to be good. So you think it has more to do with the cord than the wall if the S4 has been running just fine at full hash rate for a 5 days now? What kind of power cable would you recommend for the S4 if I need a replacement?
The S5's are completely silent now.