Switch Mode Wall Warts in Series

Perhaps the "negative" supply can't sink current? How about load resistors on the negative side so it's supplying current?

.... Phil

What's not working?

Is one end (of the output) grounded to a safety ground?

I'm with most of the rest of the group: if you can't tell us what symptoms you're seeing, we can't diagnose your problems.

If the outputs are isolated from the plugs (which they should be if it's North American two-bladed plugs), then at first blush I don't see what the problem might be.

You can't use a virtual ground IC ?

Jamie

"Tim Wescott"

If one strips the PCBs out of their boxes and wires them to the AC supply - this cannot happen

Also, you must add reverse polarity diodes to both DC outputs so overloads ( from + to -) will not result in one output being forced 12V in reverse when that PSU current limits or shuts down.

Might be *very bad* for the curcuit being supplied IF both DC rails are ever the same polarity too.

.... Phil

Old school DC adaptors with iron transformers, rectifiers & filter caps did not have the same issue - the rectifier diodes would alway act to effectively short the output if sufficient reverse current were applied.

If you just add 3A diodes ( ie 1N5401s etc ) to each SMPS adaptor's output you will probably be OK.

Good practice anytime with split DC rails.

... Phil

A Schottky rectifier from each rail to common will usually save the load from dying due to supply reversal. Otherwise, if the outputs are isolated, there should be no issue at +-12V. I'd do it myself in a heartbeat.

Cheers

Phil Hobbs

FFS, with split DC supplies the load is from one rail to the other.

So BOTH have to be able to supply the same current OR or bad things can happen.

If one is not powered OR one shuts down and the other does not ????

Get real wanker.

The OP is smarter than you.

.... Phil

If you're only building audio amps, maybe. Other things typically load the positive supply harder than the negative one.

You have to size the power supply properly, so what?

The diode prevents damage. You posted something similar yourself. Using Schottkys will protect against the ground going open as well, assuming that the diodes are on the load side of the break.

I'm not too interested in who's smarter than whom. This is a discussion group, so try to discuss rather than disgust. ;)

Cheers

Phil Hobbs

... Phil

I don't know why everyone is posting nonsense. It works fine and you don't need to add any diodes. Crack one open and you can see what a simple circuit it is.

You can also buy a nice center tapped SMPS online.