We think a good primer is this multi-layer PCB layout guide which [Rik te Winkel ... In the case of a 2-layer board these just go right through and connect the top to the bottom.

Eventually, this gave way to the aggregating PCB services ... to an inner layer, or buried vias which only connect inner layers. Example impedance-controlled traces for 2- and 4-layer PCBs.

TL;DR: NVIDIA's upcoming GeForce RTX 5090 features a 16+6+7 phase power design, 14-layer PCB, and up to 600W TGP ... it is unclear whether the 12V-2×6 connector will be introduced, including ...