And in a year or two I expect that clause will be found to be unreasonable by the ACCC (Australian consumer protection body) and Nintendo will end up getting fined for it.

Their website says that it uses USB-C for charging and the charging port accepts stock USB-C cables, it's not even remotely reasonable to bury within the warranty a statement which says "oh, by the way the device cannot accept USB-C cables -- if you use a made-to-spec cable that fits in the port, no warranty for you!".

The problem is that most consumers don’t read those warnings. And the “reasonable person” would assume that any USB-C cable would work if the USB-C-like receptacle mates with their USB-C cable.

Why would nintendo warranty try to cover scenarios entirely out of their hands? Just because the other guy claims they've produced a usb-c charger doesnt mean they actually did it correctly (which is apparently the case with these docks)

If you shove 9V into a 5V device, bad things will happen, regardless of Nintendo is anti-standard or not

Nintendo say that for all their devices, even the ones that use Nintendo-specific connectors.