Note that this is an isolated supply, but the output terminals mustn't go too far from
earth (the input-output isolation is tested to 3kV, but output-earth isolation is only
tested to 500V)
Unlikely to be a problem ... but it might be worthwhile tying "V-" to the ground terminal with a little wire jumper - give it a solid reference point.
(ie. The screw terminal for earth will have two
wires in it, one to mains ground and the other to "V-")
This trick can also save you from pain if you're using multiple power supplies and you forget to connect all the grounds together (although it shouldn't be a substitute for doing that - belt+braces...!)
I would get shocks from my bench supply because i leave Jumper wires sticking out of the Ground rail on the breadboard. Every now and then my elbow would brush across one and i would feel a sharp stinging sensation. It took a few times to realize what was going on. Probing V- wrt ground shows about a 30 volt difference :/.
This trick will help with that, too...
I've seen differences of much more than 30V. In theory you're safe to grab the wire because it's floating but yes, it will tickle you if you brush it lightly.
nb. Connecting V- to GND will take away some of that safety. If there's bare V+ wires lying around you might be better off not doing it. I don't think it's a problem for 5V/12V supplies but ... it's your decision...
The GND of Arduinos is usually connected to mains ground via your PC and I suspect you've touched Arduino 5V wires many times.