Lamp cord can be and often is larger than 18 gauge. Your expensive power cord probably has lamp cord inside or equivalent with a fancy wrapper.
As far as preaching what others can hear or not goes it's not my job to prove you can't hear the difference it's your job to prove you can. I have tried it as well as many others with even higher end systems than me and none of us are convinced. When a friend of mine had another friend who is a power cord builder install his PC in his system my friend told the PC manufacturer he could hear an improvement with the new cord. He later told me he really couldn't but didn't want to "tell the emperor he had no clothes"
As far as preaching what others can hear or not goes it's not my job to prove you can't hear the difference it's your job to prove you can. I have tried it as well as many others with even higher end systems than me and none of us are convinced. When a friend of mine had another friend who is a power cord builder install his PC in his system my friend told the PC manufacturer he could hear an improvement with the new cord. He later told me he really couldn't but didn't want to "tell the emperor he had no clothes"