Connecting power to a DC PSU on switch

[AckAck]

I have a 3850 with dual DC PSUs, -48vdc. Before I put this in the rack at a remote location, which has proper power, I want to fire it up and do some configuration on the bench. I have a DC power supply that does +48vdc and enough amps. Am I able to use this on the switch's PSU? Is it simply a matter of reversing the polarity when connecting my source to the DC PSU? 

I've read the docs on installing and replacing FSUs, the hardware installation guide, etc, but all are expecting that you're wiring up to an established -48vdc data center power supply. None deal with the basics of BYO-power supply. 

I've read that the switch PSU is DC-Isolated, meaning neither pole is connected to ground - it's a floating circuit - which is perfect. The PSU has a ground terminal, which is for earth ground. All good. My power supply has VDC+ and VDC-. It can output 48vdc, and up to 12A. Of course, with a multimeter, I can measure +48vdc when touching red lead to VDC+ and black to VDC-, and -48vdc when touching red lead to VDC- and black to VDC+. Do I simply wire the source VDC- to the PSU + terminal and source VDC+ to the PSU - terminal? 

This may be the most simple of questions, but the more I read about negative voltage, the deeper down a rabbit hole I went and now I'm questioning all my assumptions and worried about frying the PSU. Can someone set me straight? 

[AckAck · Accepted solution]

So this worked fine. I hooked up directly to the DC power supply and learned that Cisco PSUs are very tolerant of incorrect wiring. Thinking that the device needed -48vdc, I reversed the polarity between the DC supply and the PSU, since that's how my meter reads -48vdc. This caused no reaction on the Cisco 440W PSU - no lights, no smoke, nothing. I reversed the polarity back to normal (positive to positive), which would supply +48vdc to the switch, and it worked great. Lights came up green, was able to plug it in and switch came up just fine. 

I'm not too clear on what the theory is here, other than there being no difference between positive and negative voltage in a floating circuit (neither positive or negative bridged to ground) - both show a potential difference of 48v, which is what the switch wants. Anyway, it was confusing, but thanks to Cisco's great build quality and some experimentation, this story had a happy ending.