Question about Xtorm XB3 Series Titanium

I bought the XTORM XB304 (27200 mAh, 100 W). Charging phones and iPads goes smoothly and well. However, I bought exactly this powerbank because it should also be able to charge laptops - BUT: Nothing works with my Surface Pro7. Normally I charge the device on the go via USB-C/power adapter without any problems - but when I use the supplied USB-C PD cable & powerbank, Surface Pro7 does not recognise any power source. Only when I plug in and charge the powerbank itself does it seem to have enough voltage to charge the Surface at the same time. Can anyone help me out here: What do I need to do to charge my Surface Pro7 with the XTORM. Many thanks!