Okay, I seriously wanna give up on this, but knowing myself, I can't let it go. USB-C charging is a confusing mess of options and unratified standards, it feels like you're taking chances whenever you're buying a charger and HOPE that it works with the Switch.
Apple USB-C-to-USB-C cable (model A1739), Xiaomi ZMI QB820 20,000 mAh powerbank with USB-PD, Anker PowerPort+5 wall charger with USB-PD (model number A2053), Tronsmart U5P wall charger with USB-PD.
Let's get the cable out of the way. The USB-C cable? Check! Approved by Benson and Nathan.
Now the rest of the components are a complete "test your luck" kinda deal. Here's what I needed and what I found out.
What I need:
1. A wall charger that fast-charges the Switch via USB-C PD. (not a slow charge, that's universally available via any standard powerbanks or USB-A wall chargers made for cellphones)
2. A wall charger that fast-charges the QB820 powerbank via USB-C PD. (not a slow charge, that's universally available via any standard powerbanks or USB-A wall chargers made for cellphones)
3. A powerbank that fast-charges the Switch via USB-C PD, fast enough to counter battery drain while playing Zelda with maximum screen brightness, maximum volume on headphones and WiFi on. (not a slow charge, that's universally available via any standard powerbanks with USB-A)
What I got:
For #1, it was between the Tronsmart and the Anker. Looking at both of them, the both have the same charging outputs (5V3A, 9V3A, 15V2A) with the Anker having the additional 20V1.5A. The Switch fails to charge on the Tronsmart while works on the Anker. Either the Anker has the additional circuitry that the Switch detects and allows charging while the Tronsmart didn't, or the Anker's 20V1.5A charging output is the only charging power output recognised by the Switch, the other three didn't (5V3A, 9V3A, 15V2A). Am surprised that the 15V2A didn't work on the Tronsmart.
For Point #2, again it's between the Tronsmart and the Anker. This is what's confusing me. The Anker straightaway works. The Tronsmart doesn't initially, but when I swapped the Anker for the Tronsmart right away, it then works charging the QB820. WTF!!? I tested again, by unplugging the Tronsmart wall charger and replugging it into the QB820. Doesn't work again. Plugged the Anker, works straightaway, and swapping it with the Tronsmart, the same as earlier on.
Point #3, the QB820 powerbank. It fast-charges the Switch via USB-C PD fast enough to top up the Switch's battery while playing Zelda at max screen brightness and max volume on headphones with WiFi on. Also works in this case, the Anker 26,800mAH with USB-PD powerbank model, although I'm basing that on anecdotal reports on Reddit and forums I read.
TL;DR version: QB820 powerbank fast-charges the Switch. Anker PowerPort+ 5 fast-charges the Switch. Tronsmart U5P doesn't charge the Switch. Anker PowerPort+ 5 fast-charges the QB820 powerbank. Tronsmart U5P Fast-charges the QB820 powerbank (with a workaround).