I have an embedded system and one of the PCBs in the module should be connected to a 5V power supply -> positive(+) and neutral(-). The NEUTRAL knob is directly tied to the GROUND knob in the power supply. I had a power supply with the current knob turned to maximum and a set voltage of 20V.
After turning on the power supply, I connected the ground wire from my PCB to power supply's negative (-). I left the VDD wire from my PCB unconnected to the power supply, it was just hanging around. The PCB required 5V input but the power supply was set to a voltage of 20 V. I thought since the VDD is not connected to the power supply yet, it should not be a problem.
Immediately, the ground connector on my PCB sparked, causing a decoupling capacitor connected to it to badly burn out, followed by a few resistors and LTC3404 step-down converter chip on the PCB. Then I pulled out the ground wire of the PCB from the power supply.
I do not understand how the connecting of just the ground wire from my PCB to power supply neutral could cause my capacitor to burn out, even though the power supply had higher set current and voltage than required by the PCB. So, was it the current on the neutral wire that burnt out my capacitor or is there anything to do with the higher voltage?
NOTE: I have been using the same power supply and PCB with 5V and the current knob turned up to maximum, for months and had no issues before.