Honey, I blew up the RT-AC86U! (Passive PoE blunder)

[Canukhed]

Gutted and feeling very silly.

After reading plenty on the topic, for wiring reasons, I bought a pair of passive PoE adaptors
https://www.amazon.co.uk/dp/B076LR5KMF/?tag=smallncom-21
..where i planned on using the original Huawei PSU downstairs, next to my Asus rt-ac86u router and the existing cat5e cabling to power the HG612 modem in the attic where it currently connects to the incoming 'BT' signal.

I understood these adaptors would make use of unused copper in the cat5e to carry my modem PSU current up to the modem, whilst isolating those conductors from my fragile router and the modem.

With the upstairs end of the cat5e cable unplugged for now, I came downstairs and I plugged the Huawei PSU into the female PoE 'injector', the female rj45 of that injector to my cat5e cable (which goes upstairs), and the male rj45 of the PoE injector into the WAN socket of my Asus.

Immediately, the Asus lost all power and wouldn't come back.

The end.

A. What on earth did I do wrong other than trust reviews. Did I misunderstand these passive PoE setups?
B. I don't suppose there's a tiny link in the Asus which pops under this circumstance, which I can replace and be on my way?

I've already ordered a shiny new replacement router from Amazon

Thanks for any non-insulting input!

I appreciate this post because I am learning as well. The best way to learn from others is if they share the fails of their activities in order to do better in the next round. Your post is a sacrifice that will help many others. Without knowing what went wrong, others will repeat the same mistakes and knowledge and progress will be lost. Thank you, from a newbie.