Yes, I admit that I made wrong decision toward related Internet source to link only pictures (related post links are therefore disabled now). In short, from three USB power output ports only USB-C PD1 (supporting USB-DCP charging protocol only, at 5V range) one will work as expected with the Librem 5: 拆解报告：HELPERS LAB 20000mAh 60W 双PD+QC移动电源 - 充电头网 - 我们只谈充电.
In addition (while I do not think that you can find and buy above linked one) you might want to end up with ANKER A1275 (either A1275Z11 that I use or A1275S11, or smaller A1241) power bank which carries (as one of my USB testers detected there), in addition to the USB-DCP, SAMSUNG charging protocol yet as long as Samsung device not connected there it will not interfere during charging of the Librem 5 phone.
Anker A1281 is fine charging option too: Discharging a powerbank (Anker A1281). Also, I hope that I managed to make clear that my selection of power banks are based on my own expectations related to charging of Librem 5, and for example didn’t mention here (purposely) any other Anker power bank that will be OK for recharging of BPP-L503 battery cell. Mentioning few Anker power banks is related only to what and where available, and not while I like their products in general (as out there exist manufacturers that still outperform in quality many of Anker charging products easily).
P.S. Perhaps even Anker A1290 USB-C port (controlled from Cypress CYPD3171 protocol chip and Southcore SC8812A) might be another one that works with … yet I’m not about to test it ( even though it might work with the Librem 14 out-of-the-box and as most common posts here are like “I cannot charge from …” although “PD” letters written there … after reliable “review” found within “only counts” Anker community). Perhaps usage of exact RON/ROZ octane rating counts here as well 
(battery millage related)?