I also have powered subwoofers in my Vandersteen 5A's and have tried various power cords. My Three favorites are FIM/CRL Gold, FIM/CRL Silver and JPS Power AC and AC+. A good power cord on powered subs, especially when with a speaker pair, is worth the extra expense. However you don't have to get the most expensive cord with filters, shields etc. because your only powering below 100hz.
Rick
Rick