Yeah it's a high-wattage 3rd party PSU.
I've read that NUCs need a lot of wattage for the two Thunderbolt ports as well as the mid to high-end Intel processors that are available inside those Thunderbolt-equipped NUCs.
So yes... the PSU in the image I posted might not be the
typical NUC PSU.
Still though... it's kinda silly to say
"look at how small the NUC is" without acknowledging the external PSU that is required.
Could Apple make a smaller Mac Mini? Absolutely. But they'd likely have to use an external power supply. Like the NUC.