Effects Of Power Cords On Electrostatic Speakers

Several weeks ago I took delivery of a pair of Martin Logan CLX ART speakers. I hooked them up with the supplied power cords from the seller. The sound was pretty underwhelming, so I let them settle in. After about 4 days the sound had not changed significantly. I decided to rob a pair of PI Audio power cords from my phono stages and put them on the CLX. Signicant change and was getting the sound I expected. 

The question I ask myself is why? This is a low current power supply that just feeds the stators. 

If it is indeed significant, and it seems to be, what level of cord is going to meet the needs? No reason to spend more than I have to. 

Looking forward to reading your thoughts or experiences.