2 19VDC laptop chargers in series

[Daniel_LaFleur]

Originally Posted by Ether

Can someone explain what aspect of the supply's output circuitry does not like having a voltage applied across it... said voltage being of opposite polarity so that said voltage is attempting to push current through the supply in the forward direction (as would be the case we are discussing with the two supplies in series)?
[/i]

In addition to what Jason said, there is a voltage feedback to the switching controller that may not like a voltage on it's feedback input being lower than it's ground.

Originally Posted by philso

Paralleling diodes only prevent one supply with lower output voltage from dragging down the other. The supply with the lower output voltage will not be able to push out much output current since it's paralleling diode will not be forward-biased as much or may be reverse-biased in the extreme.

Mostly right. When current is pulled from 2 supplies with outputs connected by 'OR'ing (matched) diodes, the current will only be pulled from the supply with higher voltage until that supply cannot keep up. At that point its output voltage will start to droop. When it droops to the level of the second supply that supply will then take the rest of the load.

It's not the best way to parallel supplies, but it does work when 1 supply wont source enough current.