Got the numbers I needed.
Components used: Official Nintendo AC adapter, Anker PowerPort+ 5 with USB-PD wall charger, Xiaomi ZMI QB820 powerbank with USB-PD, Aukey 30,000mAh powerbank with standard and Qualcomm Quickcharge 3.0, Apple 2M USB-C-to-USB-C Benson-approved cable.
The condition:
Zelda BOTW, max brightness, max volume, WiFi on.
The figures:
Charging the Nintendo Switch using:
1. Official Nintendo AC adapter: 15V 1.25A
2. Xiaomi QB820 powerbank via USB-C PD: 15V 1.0A
3. Xiaomi QB820 powerbank via USB-A: 5V 1.5A
4. Aukey 30,000mAh powerbank via USB A (non-QuickCharge): 5V 1.5A
5. Aukey 30,000mAh powerbank via USB A (QuickCharge): 5V 1.5A
6. Anker PowerPort+ 5 via USB-C PD: 15V 0.5A *
SLOWER than QB820 powerbank!*
7. Anker PowerPort+ 5 via USB-A: 5V 1.5A
Bonus figures:
Anker PowerPort+ 5 charging Xiaomi QB820 powerbank: 15V 2.5A
Official Nintendo AC adapter charging Xiaomi QB820 powerbank: 15V 2.6A
The best combo for charging are the official Nintendo AC charger, the Anker PowerPort+ 5 and the Xiaomi QB820. Other than getting powerbanks or outdoor camping power cells and off-the-grid equipment like the Omnicharge Omni or the RAVPower 20,100 mAh 65W with AC outlets built into them, these three chargers are all I need at home and outside.
Also from those figures, QuickCharge or any other formats of fast-charging other than USB-PD does not charge the Switch any faster than your standard USB-A charger, they are not supported.