Question about be quiet! 12VHPWR

The NVIDIA Founders Edition of the 3070TI has a 12VHPWR connector. There should be an adapter included with the GPU, then you don't need this cable for the 3070ti. If you got your card second-hand and there was no adapter included, then you need one.
The be Quiet! adapter is only for be Quiet! power supplies and the only advantage is that you can be sure that the quality is right.

You only need this cable if the graphics card is close to the max of 450 watts, which is the case with my rtx 4090... the cable probably supports 600W according to the labelling....

You do not need the cable for the 3070 Ti, the card does not have this power connection.