The Capsule need 15V DC. It states needs 3A also but that’s probably peak corner case and less than 3A will work in some situations like say when it’s powered off or to slow the discharge.
15V you can get a few different ways.
A 5V to 15V conversion cable, mentioned above. It needs 5V input from a 5V portable charger.
A 15V capable portable charger, and a PD sink which select 15V.
Until someone who owns either lists the products used, nothing is verified to work. Just explaining why it won’t simply work just because some portable charger can do 15V does not mean it will do 15V. How the hell would it know from 5 9 12 15 V which to use?
If the Capsule was different altogether, say it came with a 15V PD charger then the PD sink was within the Capsule. It doesn’t. It’s a 15V DC.