As per Green0Photon's link, Amazon has the Anker Powercore Speed 20k back in stock. Which surprises the heck out of me, since Anker no longer has any mention of the battery on their web page.
This really is the battery for the Vive wireless adapter. Note that you can't just look up "powercore," since Anker labels a half dozen different models with the "PowerCore" name, from plain-vanilla USB batteries to the 60W PD "Powercore 26K for Laptop." If you want the QC 3.0 version with 2A @ 12V, you need the "speed" version of the PowerCore specifically.
I got this one for about 20 bucks less than the one you have posted. THe only major difference is that mine doesn't support USB-C like the one you chose seems to.
Still, generally they're great products. You can't go too wrong with most of them.
I bought it in March from Amazon -- apparently a different model, but it's been working for me with the VP2. And I'm pretty sure it does say the 1.75A or whatever on the bottom.
Granted I haven't used it a ton, I've been pretty busy. But it's definitely fully worked for a few sessions, whereas using an 18W battery barely works for a few seconds.
I bought this battery off a recomendation from reddit before. This the one you were talking about?
https://www.amazon.com/Anker-PowerCore-20000mAh-Qualcomm-Recharging/dp/B01N0X3NL5