Unusual Power Supply (Wall-wart) Labeling

Thread Starter

Jon Chandler

Joined Jun 12, 2008
I came across this power supply for an IBM laptop at the thrift store - couldn't pass it up for a couple bucks.

But instead of the typical rating of x volts at y current, it's labeled like this:

16 - 10 Volts

2.2 - 3.2 Amps

It's a single output supply, with two conductors.

Most wall-warts are fixed voltage. Increasingly, some wall-warts are constant current for powering LEDs. This one is a bit of a mystery.

ibm power supply.jpg


Joined Mar 10, 2010
I wonder if it negotiates the power like USB PD. I would have expected more wires if it does.

Or maybe it's a regular power supply but for some reason had to give it a rating based on two different loads.


Joined Mar 10, 2019
It seems to be an "unregulated" power supply. That is, at 2.2A, the voltage will be about 16V. Once you draw 3.2A, the voltage will drop to 10V.
But, that seems a bit of a large range to me. Many capacitance filtered wall-warts will show this type of behavior.
Are you sure it has only 2 output wires? If there is a 3rd wire, it may switch the voltage upon detection of the laptop.


Joined Oct 2, 2009
Transformers have internal resistance that causes the output voltage to fall as the current increases.
A transformer rated at say 10VDC would output about 16VDC with no load.
This is saying that it can deliver 2A at 16VDC and 3A at 10VDC.

Thread Starter

Jon Chandler

Joined Jun 12, 2008
Of that, I am well aware.

This is a switching power supply, which usually are pretty tight in their regulation.

Also most switchers, when pushed too hard, drop their output voltage, so the current falls.


Joined Mar 19, 2019
Look at the input specs. It is rated 100-240V 50/60Hz. I would expect that based on the input voltage the output voltage would differ. Apparently unregulated and dependent on regulation within the supplied equipment.

Delta Prime

Joined Nov 15, 2019


Joined Jun 5, 2013
I suspect that it is just a normal switching supply that can produce 2.2A at 16V. Unlike others though, they chose to characterize what happens at higher current.



Joined Jan 23, 2014
16-10V is puzzling, unless it has some characteristics of a battery charger with constant current/constant voltage modes. That could have some advantages over charging batteries from a fixed input voltage.