For proper operation for units with the USB-C power port, a power delivery adapter capable of delivering 20V, at a minimum of 2.25A (45W), is required. Most USB-C PD adapters sold are usually rated for 60W- which is more than capable. Just make sure it shows 20V as an output. DO NOT try to use a USB-C 5V phone/tablet charger. It will not work.
Here are a few examples of compatible adapters sold on Amazon:
USB C Charger, RAVPower 61W PD Charger (link):
USB C Charger,AUKEY Focus 60W PD 3.0 Charger (link):
USB C RAVPower 20000mAh Power Bank 60W PD3.0 (link):