RepOne uses USB-C for charging. USB-C is great because it's reversible, charges fast, and it's become a very common format. However, there are different types of USB-C cables and not all of them work with all devices. You may have tried out your phone or computer charger and found that it didn't work with RepOne. The simple solution is:
When in doubt, use the included RepOne charging cable.
The included cable is USB-A (charging brick side) to USB-C (RepOne Sensor side). Most cables like this will work to charge RepOne, but when in doubt you should always switch back to the cable that came with your unit as it's guaranteed to work.
Most power sources work as long as you are using a compatible cable. If you don't see any charging indicator on the device screen, make sure to update your firmware to the latest version so you can instantly see if the device is charging.