Hi, my circuit board is powered by a switching power supply which outputs 12VDC. I put the scope probe at the COM output terminal on the power supply (setting scope to 1sec/div on the timescale) and it shows a very noisy ground - zigzagging nearly +/-1V from 0V. As a result my whole board is noisy. When I move to a different wall outlet (closer to the subpanel) it's so much cleaner. My circuit cannot depend on how noisy the wall outlet is. How do we "filter" ground noise on the circuit side? Thank you!