I have three Samlex SEC-1223 power supplies, and I’ve had to modify each one to be less noisy. I’m surprised you don’t have a problem with the SEC-1235. I’ve modified all three units: 1) FT50-77 toroids on the AC lines from jack to board. 2) Ferrite beads from the board to the power jack. 3) Bypass caps across the power output 4) Grounding case to the station ground Without it, there were a lot of strong birdies on 160m.