Incidence of vias in the middle of a net
If you want significant power supply current to flow through a via, you must make sure that it has sufficient total copper area. You can ask the PCB manufacturer what the minimum wall thickness is for their vias.

When I've designed boards, I've usually assumed that with standard processing, so starting out with 1/2oz / 17um copper plating up to 35um, the via will end up with at least 17um wall thickness as well. This is probably optimistic, though the via is very short and is heat-sunk by copper traces at both ends, so is unlikely to overheat even if it is a bit thin. 

A common technique is to use multiple parallel vias when you have significant current flow. If concerned, then compare the voltage drop along a few mm of a high current trace with the voltage drop from one side to the other. If the latter is excessive, then you need more vias. 

If you treat a via as a piece of track which is twice as wide as the via, then it's probably about right. If the track needs to be wide to carry your current, then connect it with as many vias as will fit into the width of the track.