According to specifications: Scope of delivery Micro USB cable

The description mentions Micro USB.

Wouldn't your question be better addressed to the Samsung S8 product? My iPhone charges faster with the Cellularline than directly from the socket.

Yes, there is actually nothing to be said against it. Perhaps an ultra-flat power bank would be even more suitable for wearing with a heated waistcoat, but that also depends on the waistcoat.

...infinite to defective!

Cellularline Freepower Slim Horror-Fazit Digitec-Test: Wird mit FastCharge beworben, obwohl sie maximal 10 Watt aufnimmt, was jede Powerbank kann. Wird auf der Verpackung mit übertriebenen Leistungsdaten beworben: «Smartphone 8x laden» – welches Smartphone hat eine Batterie mit mickrigen 1250 mAh? Selbst ein Nokia 8110 speichert mehr Energie. Siehe empfehlenswerter Digitec-Test hier: https://www.digitec.ch/de/page/welche-powerbank-hat-wirklich-power-12991 Power-Bar-Empehlung am Ende Test: I've chosen the Xtorm XB303 as the one to keep. It's the combination of high capacity and fast charge/discharge that wins it for me. In the >20000mAh category, the only other competition is the Anker 27000mAh power bank (plus variant) but the extreme slow charging rules it out. Plus, around 15W/18W where my phones will usually charge, the Xtorm has a higher capacity.

Theoretically, it would be possible to connect the same powerbanks in series. There seem to be some powerbanks with pass-through functionality, but in reality I have never encountered or used this. On the contrary: the electronics of most powerbanks are too stupid to charge and be charged at the same time. Would rather buy a bigger powerbank.

should also work without

According to our own research, the charging capacity of this powerbank is too low. Da empfehlen wir solche hier: https://www.digitec.ch/de/s1/producttype/powerbank-2040?tagIds=82-537&rng=23-230%3A21.001%3A%7C23-230%3A15.001%3A21.001&pdo=20-15988%3A304319%7C20-15988%3A304313%7C22-14834%3A331553 .