I think it's a pretty reputable brand over all, someone on the gpd discord channel recommend it. I also grabbed this https://www.amazon.com/dp/B07N7Z6LSC/ref=cm_sw_r_cp_apa_fabc_6Lp3Fb3Z7ZJDX since it's a 65w power bank as well. Basically doubles the win max battery life on the go, also charges up super quick.

I just found this beast. I think this is the best we could hope for! PPS for Super-Fast Charging as well as PD maxing with 20V at 3.25A, the same power provided by the included AC Charger of the WIN Max!

ZMI PowerPack 20K Pro USB PD Backup Battery & Hub (USB 2.0 Data) 65W 20000 mAh Power Bank with PPS

https://www.amazon.com/dp/B07N7Z6LSC/ref=cm_sw_r_other_apa_i_wOc2Eb0M4EAPD