Any Quick Charge 3.0 power adapter will work, as the powerbank can not only fast charge smartphones, but the powerbank itself can also be charged with the QC 3.0 fast charging standard.
The charging time is halved if you charge the powerbank via the micro USB port with Quick Charge 3.0.

I am currently using the supplied cable and an Apple iPad 12W adapter.
I am wondering myself how best to charge the powerbank.