Hi, Guntherkai
Based on your requirement of 1500W and ATX 3.0 compatibility, I'd recommend TOUGHPOWER GF3 1650W.
Regarding the concern of cable length, the included cables are 600 mm, the cable of ATX 12V for CPU is even 750 mm. In Tower 900, which's overall height is 752 mm, the cables should be sufficient to reach the upper-middle position of M/B. However, it really comes down to how you route your cable. In some extreme situation, you might need a extention.