I have 2 laptop power adapters (Dell) that are 19V @ ~3A. I'm curious, if I connect the + output of one to the - output of the other, will that generate a +/-19V supply (with the center/virtual ground being where the outputs connect)?

Both adapters have 2 prong plugs and the 2-pin figure 8 connectors so there's no earth connection.

My hope was to run then this into an LM317 and an LM337 regulators to generate +/- 15V power sources.

Just wondering if this is doable.

 

Both adapters have 2 prong plugs and the 2-pin figure 8 connectors so there's no earth connection.

All of those adapters are switching regulators these days and don't use transformers for isolation from line voltage.

Do a resistance check from +/- terminals to both prongs on the plugs. If they're isolated, you're good to go.

 

They will be isolated otherwise they would electrocute the laptop operator.
Yes , you can connect them in series as you propose.

 

I agree, I’ve used two switching 12v wall warts for +/-12v in a pinch. Tie them together and check it with a meter.

 

All of those adapters are switching regulators these days and don't use transformers for isolation from line voltage.

? ? ? WHA ? ? ?

At 60 W with no earth ground pin, they are 100% transformer-based, with reinforced insulation and extra-wide creepage and clearance distances.

ak

 

All of those adapters are switching regulators these days and don't use transformers

No, they likely have a switching regulator that uses a high frequency transformer with isolation between the primary and secondary.
All approved power supplies have isolation between the mains and their output.

 

Check first if are floating.

I doubt. I believe the negative is connected to ground

 

Check first if are floating.

I doubt. I believe the negative is connected to ground

They have two pin supply plugs so there is no ground connection.

 

All good supplies should be isolated,
and Dell are a good make,
but it is known for "grey " parts to be connected to the neutral of the mains.

Once had a TV , with an external supply, it had 110 V on its SCART plug, till the SCART was plugged into an earther VCR )

 

If you measure the voltage between one of the output pins and ground of an isolated SMPS with a high impedance voltmeter it will typically read a high AC voltage. This due to the capacitance between the primary and secondary sides of the supply but as the capacitance is small the available current is very small. Enough to show on the voltmeter but not enough to harm you.

 

They have two pin supply plugs so there is no ground connection.

It's not a protection ground connection that's of concern, it's whether the output is isolated from the mains voltage.

 

It's not a protection ground connection that's of concern, it's whether the output is isolated from the mains voltage.

I do not believe that there are any laptop supplies which are not isolated by design.
Show me one.

 

I do not believe that there are any laptop supplies which are not isolated by design.
Show me one.

I agree, there is not likely one.
But that wasn't my point.
Whether the mains power is two pins or three pins has nothing to do with the question of isolation.

 

I agree, there is not likely one.
But that wasn't my point.
Whether the mains power is two pins or three pins has nothing to do with the question of isolation.

I was replying to:

I doubt. I believe the negative is connected to ground

 

I was replying to:

Okay, my misunderstanding.

 

In case you're interested: There is a recent thread in this section by SamR about this construction of a dual tracking supply, which I think contains the schematic he used.