I owned four ARC phono preamps (PH7, Ref 2, Ref2SE, Ref 10 Phono). The stock power cords are quite good actually. If your unit is new to you, perhaps use it for a while before changing the cord. I also used Shunyata power cords and interconnects with all of those, and each responded to the benefits the cords and wires provided. You won't make a mistake with whatever Shunyata power cord you choose.
When I reviewed the PH7 in 2006 (here) that was with a Shunyata Taipan Helix power cord and the combination worked well. The Taipan Helix was, iirc, the third model down in Shunyata's lineup at the time. The PH7 doesn't really need an 8-gauge power cord. You may want to consider whether the PH7 can manifest full benefit from all the features in a cord such as today's Alpha. I wouldn't hesitate to consider the Delta or Venom series with the PH7.
Fwiw, the PH7 definitely benefits from NOS 6DJ8/6922/7308 tube substitution. Say a nice Amperex 6922 circa 1970's.
Thank a lot for your answer. I bought my ARC PH7 when I was living in Brasil and the stock power cord was for their standard. Now I came back to Europe and I need a shucko model. All my gear has shunyata alpha. Only NR is on CD. I think I will borrow an EF from my dealer. The DELTA might be a good choice and I will try to listen to it. It’s cheaper than the Alfa and that can be a factor of decision.
And yes I have change the tubes for a Phillips NOS Miniwatt. From 68, I believe, with great results! I also have an Einstein Audio The Turntables Choice, SE. The NOS tubes gave the ARC PH7 the margin to win against the TT choice. Great tone!