Your description misses me. Drawing, please. It sounds like you are describing more leads than I have. I have one ground. One power input, which I can measure with the meter. One input.

No, just two leads.
Connect the meter ground lead to the supply minus voltage.
Connect the power (+) input to the power supply common.
The meter thus has a plus voltage from its input to its ground, as is needed to measure the voltage.
Shouldn't need a drawing for that.

 

No, just two leads.
Connect the meter ground lead to the supply minus voltage.
Connect the power (+) input to the power supply common.
The meter thus has a plus voltage from its input to its ground, as is needed to measure the voltage.
Shouldn't need a drawing for that.

Re: "Connect the meter ground lead to the supply minus voltage."
But then that minus voltage would read as ground.

 

Re: "Connect the meter ground lead to the supply minus voltage."
But then that minus voltage would read as ground.

No.
Don't get hung up on the word "ground".
"Ground" or "common" are just labels for a voltage node reference point. It has no special properties otherwise.
So the voltmeter will read the voltage between the ground node and the minus output node with the ground node being positive with respect to the minus output node.
To the voltmeter that's no different than measuring between the plus output node and the ground node.

 

No.
Don't get hung up on the word "ground".
"Ground" or "common" are just labels for a voltage node reference point. It has no special properties otherwise.
So the voltmeter will read the voltage between the ground node and the minus output node with the ground node being positive with respect to the minus output node.
To the voltmeter that's no different than measuring between the plus output node and the ground node.

Too limited. I'll stick with my inverter for now.

 

If you use the power supply ground as the plus input to the meter and the minus voltage connected to the meter common, then you should be able to measure the negative voltage as well.
It just won't have a negative sign in front of the readout.

Here's one that measures either plus or minus voltages with 1mV resolution to 19.999V.

I got one of the Drok meter you suggested. It works as advertised. 4-wires, no hook up instructions but that wasn't difficult. Red positive 5 V, black ground for power. Yellow -V to +V input. Blue is input ground. Like the others, it cannot measure a voltage between two points. The blue wire must be ground. Again my differential front end comes into play.