There are some power banks that will not work with the EtherScope nXG.  The PowerArc ArcPack PA1801 is a recommended power brick because:

1. It is 54Wh capable for 100% charging the 46Wh EtherScope (some efficiency lost) so well matched in terms of capacity.
2. This is also a USB-C brick which matches well the the EtherScope power adapter.
3. It is also well made (aluminum case) and uses premium Samsung cells.
4. The real bonus is it comes with a high quality USB-C to USB-C cable that works well with ES. 

While there are likely other ones that will work, the above has been tested to work with the EtherScope nXG. Keep in mind, the unit uses basic USB-C high power charging.