Is anyone in the US making power cables like this custom PC cable ad on the Canadian Mart?

Just be aware the seller did not say the conductors were also made by Furutech, just the connectors.  I also like those FI-11 connectors and use them for my own power cables.  There are a variety of good bulk power cables you could purchase in order to make something yourself that could be just as good or better, if you are inclined.  However, a quick search indicates there may to be less available bulk cable than there was a year or so ago.  If I were looking for an inexpensive option, I would consider the double shielded, 9.8 awg "Gotham 85055 Powercord (Deep Cryo Treated)" at Take Five Audio for $10.99/foot (or its smaller brother for less), but there are many other options from other vendors.  There is no requirement to use techflex on power cables and the quality of that material makes no sonic difference when used to cover the thick PVC typically used for the outer covering of power cables.
BTW, when the seller talks about, "conductors terminated with copper forks" they are referring to these types of skinny fork spades, which actually work quite well compared to trying to twist and "fork" heavy gauge wire so it can be clamped in the Furutech style connectors. 
I only saw " crimped with forks" in the ad you linked but if you want to utilize "pneumatic" crimping, I use this inexpensive hydraulic crimping tool on spade connections and it works great.  I believe a ratchet type crimper could also work well for the small spades suggested.

You think that getting a good sound is just putting a wire and connectors together than you live in a stoneage.

Uh, that’s how cable companies start, and short of the folks using special network boxes or maybe special cold weld connection techniques, most of them are doing exactly that....putting wire/cable and connectors together.  I have been inside of more than a few well respected cables and as long as you can get the same wire and connectors you can achieve the same result.  It is far from the rocket science those companies would have us think it is.  The wire/dielectric/geometry combination needed to achieve the desired sound is probably the most difficult part and yes there is a lot of research put into that by some well respected companies but, you can easily purchase the exact connectors used in multi-thousand dollar cables so, if you can get the wire in bulk....

Many of the very expensive cables have also a magic box. What do you think is in it?

Maybe stuff like this...that was duplicated by an enterprising DIY'er here.

If you want to make a good cable look at anti cables. Their best power cable is $300 and sounds $500. If you can beat it with your DIY than you are on a good path but you can not spend more than $100 in parts.

My DIY power cables made from Furutech FI-11 connectors and really old wire that cost less than $100 sound better on my amplifiers than the $1,300 Isoclean Auto Focus power cables I also own.  Bulk cable from Furutech comes with their in-house treatment and can sound very good when used with some of their well constructed connectors, but it will cost you more than $100.  Bulk cable from Neotech can also be very good although I believe they have reduced their bulk offerings in the past few years.  However, you can purchase bulk custom stuff like the C-MARC cable from Less-Loss.

I agree that some of the very top end stuff would be tougher to duplicate and that a DIY'er would not be able to duplicate the special manufacturing processes many of them use, but using the available high quality bulk cable and connectors can get you well into the range where you would pay thousands for similar sound quality.  Take some cables apart and you would see it it mostly wire and connectors.....and sometimes a crappy soldering job.

Did you compare your DIY with reputable brands?

Yes, as I posted below, I still own a pair of $1,300 Isoclean Auto Focus power cords that were favorably reviewed and that I use on my digital gear. The cables I made that sound better on my amplifiers consist of dual 10 awg wire bundles to each pole, so 2x10 awg = 7 awg to positive, another 7 awg to negative, and another 7 awg to the ground, with the positive and negative runs set up in a twisted star quad design to reduce inductance, which is a good thing for both speaker cables and for power cords. Please note the highly rated Triode Wire Lab “Seven Plus American” power cord uses the same NOS Western Electric wire to achieve the same 7 awg, and the same FI-11 connectors, with one difference being that Triode Pete’s family braids the cables rather than twists them in a star quad design as I do. I cannot link you to the exact picture of the DIY cords but they are in the seventh picture from the end of my virtual system pictures here on Audiogon.

In addition to the Auto Focus power cords, I have tried other "manufactured" power cords by Cardas and others. The DIY cables I have made using high quality bulk power cable by Furutech, Neotech, and Oyaide, and a variety of (mostly Furutech) plug and iec connectors, sound as good or better than the manufactured power cords I have tried. I have tried to show you what has worked for me so at this point, you can either try some stuff for yourself or continue to pay for manufactured cords. Not everyone wants to build their own cables and I get that so good luck whichever path you choose.