The best power cord that we have found on the Ref 9's so far has been the Synergistic Research Active AC Master couplers, which made a huge improvement in soundstage, imaging, and bass response over the stock power cords. NONE of low cost cables ( Diamondback, Viper, JPS GPA, S/R Classic AC, etc) we tried were any better than the stock power cords on these wonderful amplifiers. Hope this helps....