Is power cord upgrade now still necessary?

Thanks for the replies. I agree that power cord upgrade can make huge difference with DAC. I upgraded my DAC power cord from Cardas Golden Ref to Nordost Valhalla and the difference is huge. And I am sure PC upgrade for CD transport will be nearly equally effective if I use normal digital (metal wire) interconnect. I just wonder if anyone who use ST glass digital interconnect has CD transport PC upgrade experience?
I swapped Valhalla PC from DAC to CD transport (with CARDAS Golden Ref PC), the sound will not be as good as before. I am not sure if the reason has anything to do with ST glass cable. When I use Transparent Ref digital cable, the difference seemed not that much by swapping the PC between CD transport and DAC.
I use Theta David transport and Theta Gen Va 24/96 DAC. The are quite old, but I like their sound.
Thanks!

Nsgarch,

Thanks so much for your kind reply. I happened to use Meitner ST cable. There are 3 of them in different color, supplied with a EMM CDSD & DCC2 combo. I am not sure if they are made by Aural because I can not find "Aural" trade mark printed on the cable (nor the EMM trade mark). This is my first time to use ST cable so I do not know if it is better than other ST or not. Do you find any coax digital cable which is nearly as good as your ST in your system?

Anyway, here I find THE right person to ask my question: When using ST cable, do you think upgrade CDT PC can be as effective as when using conventional digital cable? What PC do you use for your CDT? What is your upgrade experience?

Many thanks