Power Conditioner vs A/C cables


Here's my question...Is it necessary to buy expensive power cables downstream of a high-end power conditioner?
What do they do that hasn't already been done?  As long as you don't go so cheap you degrade the signal.
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Up until a couple weeks back, I had an old Shunyata Venom power conditioner that I’ve had for years and never really believed it made much difference. My dealer asked if I’d be willing to help him break in a new Denali 6000S conditioner. All I can say is holy crap...the sq difference was immense out of the box. I’m not dialed in to all the audiophile terminology, but everything was shockingly clearer, the noise floor seemed to disappear, even seemed to add more specificity in placing musicians in the soundstage. Great sales pitch as there’s no way I’ll be able to let this go.
PS Audio offers a line of power generators that suits most budget needs. The after market AC power cords will benefit them because these generators are more like amps than conditioners. I have the P15 and use a AQ power cord and they work great in my system. 
Would it be necessary to use a power conditioner if you use a portable power supply like Eco Delta and the likes? AC noise from your appliances or anything else in your home would be isolated as the unit would only be plugged in to charge. Any ideas?