Finally I manged to replace the cables (indoor side only) for my unit. The ones that initially came with the unit were quite flimsy and I had a lot of connection issues and had to improvise something in the meanwhile. The new ones that I bought now are from a local distributor.
Delock 66023 [Delock Passive PoE Adapter Set RJ45 DC 5.5 x 2.1 mm]
https://www.delock.com/produkt/66023/merkmale.html
I also bought a Delock 82197 [Delock Cable USB Power > DC 5.5 x 2.1 mm Male 1.0 m] because I power the device straight from an APC SurgeArrest outlet (PM6U-GR) which has two USB ports.
https://www.delock.com/produkt/82197/merkmale.html
Late Edit Note: Be aware that the power rating for Delock 82197 is only 2.5 watts (5VDC – 500 mA).