I use this power bank!
It uses usb type c to charge my switch and it can charge even while playing a game that drains the battery quickly like Zelda BOTW!
I can get about 4 - 5 charges for my switch adding an extra 12 - 15 hours of play on the go
Anker PowerCore+ 20100 USB-C, Ultra-High Capacity Premium Portable Charger, 20100mAh External Battery, 6A Output Type-C Port for Macbook, Nexus 6P/5X & PowerIQ for iPhone, iPad, Samsung & more