Is there any reason to utilize upgraded power cables with these (Furutech plugs, DH Labs cable)?
No. There's no reason to utilize "audiophile" power cables in any situation whatsoever.
They are complete nonsense. Home audio is literally the
only comparable field of electronics where claims about the necessity of special power cables are being made. Scientific equipment used to make groundbreaking discoveries by measuring ridiculously tiny signals, requiring mind blowingly good precision and noise rejection, does so using bog-standard power cables.
The whole industry of these cables is just an unscrupulous money grab, praying on people's wishful thinking.
Isn't the linear power supply where all the magic happens?
Linear power supplies aren't special. The "magic" happens in the audio gear itself. Post regulation, filtering and PSRR.
If your DAC or streamer are designed to perform audibly "transparent" when powered by an SMPS, you'll gain nothing from "upgrading" to a linear supply.
Of course you'll still might hear improvements, but that doesn't mean there actually are any. Our brains are very good at fabricating those kind of things. It has nothing to do with skills or intelligence. Just a part of being human.
EDIT: Boy, did I use a lot of quotation marks in this post! I feel like Dr. Evil