Bench testing strange power supply behavior testing MRAM board - followup

FROM TIME TO TIME, BENCH SUPPLY SHOWED ZERO POWER DRAW

I was puzzled why this occurred yet 3.3V appeared on the output line going to my PCB. I originally ascribed this to buffer capacitors not needing energy pumped into them for a period, but this didn't really satisfy me. 

DISCOVERED THIS IS A CONSEQUENCE OF LAPTOP POWER BRICK CONNECTION

The test setup for the 1130 MRAM core memory replacement board used an Arduino Due to drive signals onto my PCB, a bench supply to deliver the +12V that will eventually come from the 1130 computer, a prototyping tool that provides the 3.3V pullup for the open collector sense output lines of my board, and an oscilloscope to capture the behavior of the board under test. 

The Arduino gets its power from the USB cable connected to my laptop. The ground of the Arduino, bench power supply, prototyping tool, oscilloscope and my board are all tied together. The odd behavior occurs when I have my laptop plugged into its charging brick - somehow this is causing difficulties but if I just run the laptop on batteries all is well. The brick must be driving energy into the test system somehow. The laptop is a Lenovo L340.