First post here & I have to chime in. I'm always amazed when people state that all you need is stock OEM power cords on amplifiers. It's the easiest of all the components in a system to audition. Pull out what you have, replace it with a quality power cord from a reputable audio cable manufacturer, then listen. If you don't hear any difference, then fine...
I have a C2700 Pre & MC611 Monos and have Cardas Beyond XL power cords on all the McIntosh gear. I removed ONE Cardas Clear Beyond XL power cord from the C2700 and replaced it with the stock cord. Result? Not subtle. Worse in every single category of audio definitions that I can think of.
Back in the UK a long time ago, I used to be area manager for Marantz. This was at a time when we first started seeing Monster Cables being used. I used to work the audio shows, and pretty much every single manufacturer was using aftermarket cables. Go to any show today and you will not find a single demo of any amplifier company using their own OEM cables.
What's in the box is a courtesy cable; yes, it will work, but like a lot of things, you can do better. If they included a high-quality power cord, they would have to charge for it, and since I know of no manufacturer that does this, I guess there's no business model supporting that idea.
Where we live in an HOA we have particularly bad electrics, sharing the same power line with other houses. I had dedicated 20-amp lines installed for both front end and back end, and still it sounds better when I plug the MC611s into the PS Audio P20 PowerPlant, despite McIntosh stating that their amps should be plugged directly into the wall. In my opinion, it's not about the last 6 feet, it's about the first that connect your gear to the AC supply, particularly with regard to amplification.
We also have appalling acoustics to boot, so a whole bunch of ASC tube Traps were also necessary, and yes, unsurprisingly, room acoustics dominate everything you hear, no matter what you paid for your setup.
Also, a good dealer will have multiple cable looms to audition in their dem rooms (the best place) unless you are lucky enough to have a completely treated dedicated listening environment such as Soundproofing (asc-hifi.com). If not, the Cable Company has an excellent loan program available if you are interested in trying out quality cables.