Is negative 12 volts on PSU Usable?

[cooperhero]

Read my 2nd edit for my test results, it does work!

I am trying to build a 3D printer, and have a couple of old 350w ATX power supplies.

I want to use 24V for the heaters and motors, which could be created by -12V and 12V.

The PSU's say they have 0.1 amps on the -12V rail. Does this mean they can only output 0.1 amps when using the -12V rail, or does it depend on the amperage of the other rail they are connected to, and 0.1 is listed as a placeholder value?
EDIT: 0.5 amps, not 0.1

Thanks for any answers, I would like to be able to use these an not have to buy a new power supply.

EDIT: it probably wont work with the higher amperage, but ehmkec has inspired me to test it myself anyway. Will try to do it this weekend if I have time.

EDIT 2 - TEST RESULTS: I tested the PSU with some low resistance 5W resistors, and was able to draw 2.4 amps (did not test higher as that used all my resistors) at 8.5 ohms. The voltage did drop a little from 22.5V at .5 amps, to 20.5V at 2.4 amps,

 

[jay32267]

This means that the -12V rail can only output 0.1A.

It doesn't matter what it is connected to.

So....if you connect to the +12 and -12....the most you want to draw is 0.1A.

 

[Zerk2012]

The -12 volt rail is just a negative connection and is not factored in when buying a power supply.

 

[ehmkec]

What a great project to undertake. But you cannot call yourself a tinkerer until you blow something up. You should have a good multimeter with the ability to measure current. Hook it up with a load (fans or something) and measure the amperage. Follow the instructions in your multimeter manual. Wear safety glasses.

I tried to make a guitar amplifier out of a round-top old radio when I was a kid back in the 60s. I actually got it to work - the first distortion amp ever made but I also electrocuted myself and blew the house fuse.