speedywiz: ahh, thanks now it makes sense... so if I have a freeview box connected to the LNB, then it will always be pumping out 18Volts to the LNB, and anything else connected to the same satellite cable trying to get Vertical polarity (V) pushing out 13V will be useless, because 18V is higher...
what if one set top box sends 13Volts (for vertical) and another 18Volts (for horizontal), does that mean the average? 15.5V? meaning they both stop working?
Depends how you split the signal.
If the cables were spliced together (ie. not using a splitter) then you'd get the max current being drawn from the 18 V box flowing to the 13 V box, probably frying the power supplies in one or both boxes and making the cable a little warm.
Most splitters prevent that. They send either the highest voltage from all connected boxes (all-ports-power-pass) or the voltage from a particular leg of the splitter marked power pass (single-port-power-pass).