UPDATE (Dec 15th 2018): This works on the Wii as I finished testing it today (Dec 15th 2018)...
https://www.amazon.com/StarTech-com-SATA-Drive-Adapter-Cable/dp/B00HJZJI84
you just need your own 2.5" hard drive to connect to it. it's got about a 18" cable on it which is nice for the Wii and it does not feel cheaply made.
NOTE: based on the StarTech website that device I linked to supports 2.5" hard drives up to 900mA power draw. I have only tested up to 700mA on the Wii itself. on a side note... chances are you will receive the adapter faster ordering it from Newegg's website than Amazon as it took me 9 days to get it from Amazon which is simply too long as I figure 7 days MAX and with Newegg I would imagine 4-5 days is more typical.
for a Wii... 500GB to 1TB is a bit overkill in my opinion as there is no where near that volume of games worth playing when most games are about 4GB tops which even if every single game you got is 4GB that's at least 125 Wii games or so (for 500GB hard drive, double that for 1TB) and there is no where near that many worth playing if you ask me. I figure 160GB is decent (like not a small amount of storage space) and 250GB is plenty and probably more than enough to play all of the good games for the system as even at about 4GB a game, which is typically the max, you can get at least 40 games on it with 160GB of storage space. or... with a 250GB hard drive that's about 62 games at the least. but if you can get a 500GB for cheap enough, then you can't really lose as you can always partition it if you want for Wii use for say 250GB and use the rest for general PC data backup etc if you want to.
p.s. but with all of that said... I read recently that one person who's moded plenty of Wii's has had good luck with the WD passport brand of external hard drives which is this post here...
"Wii is picky. I have seen a drive that works on one not work on the next. I have hacked at ton of the things. I would be careful about which HDD you pick up as it's hard to tell what works.
Those WD passports ALWAYS worked for me. Ive done at least 50 consoles. Probably a lot more. And you can get an old HD because USB 3.0 won't help the Wii." - mikefor20 (from Nov 7th 2018)
source =
https://gbatemp.net/threads/hdd-wii-problems.522692/#post-8367820
