RAVPower and Anker are good brands. These power banks are handy. I rarely use mine (since I keep my devices well charged), but when I've had to press my power bank into service, it works great.

The one I have is probably not made any more (1-1/2 years old), but it is a 12K model by RAVPower that I got for $17. I picked this particular one for the best balance of cost per power unit and physical size, with a trusted brand name.

https://www.amazon.com/gp/product/B01LYX73Q3/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1

All of my charging needs are met by products made by either Anker or RAVPower. You can find cheaper brands, but these two are top quality and only cost a little more than the junk brands.