@Helldiver 

This power supply should work just fine with E4.

In general, when looking for third party charger (or power supply), to avoid any issues make sure it has the following:

1. Same voltage as device you plan to charge it with.

In this case, it is 12v on E4 and 12v on power supply - pass.

2. Same or higher amperage than device.

In this case, it is 1A on E4 and 2A on power supply, 2A is more than 1A - pass.

Note that if charger has lower amperage than device, on top of other problems with that the charger may overheat - you really don't want that.

-------------------

Note that E4 consumes 12W = 12v x 1A

This power bank is rated at 36W, which means that fully charged it can support E4 running at full utilization for 3 hours. Not for 10-12 hours as their marketing material implies.