I would like to replace my monitor power supply it's 12V 3A and I doubt it's actually necessary -- old LCDs were pulling that current and this is not CCFL but LED. So I would like to measure the current drawn. The supply and the monitor is using a simple 5.5mm / 2.5mm plug, central positive. I would like to not damage anything in the process :)

OK, so presuming I have an extension cord (I do) I am ready to throw away, I guess I need to cut the cable -- does it matter which conductor? Just cut one of the conductors and touch the tips to the cut sections and done? Wrap perhaps the conductor around the tip for better contact.

Edit: so it seems my motivation matters and it got lost in the comments. A 3A adapter means it's an adapter with a separate AC cable. That's not particularly helpful for travel, especially not when even my Lenovo laptop 65W charger is now available in a small wall wart format (FSP Twinkle btw). 12V 1-2A very small wall warts are readily available. I have yet to something in a similar small format for 12 3A. I am not sure why but such a thing is unavailable AFAIK. I don't want to haul around AC cables. And yes, hacking a *very* small 12V 3A adapter with a fixed IEC C7-Nema 1 plug is a possibility but what about not hacking? :)