I’m not wanting to start anything and the fact you built your own Switched Mode Power Supply says you know something about electronics. But I would not rule out the SMPS so quickly. I wish I could troubleshoot further, but these situations tend to be very device specific and it would probably turn into a rabbit hole online. I have built my own multi-voltage/output PSU’s but all are linear with multi secondary transformers and never have any problems. It’s been my experience that some digital audio devices are sensitive to EMI from PSU’s.
Could it be that you’re stressing the regulators with the added devices and inducing EMI from the SMPS or other areas? Looking forward to what might be causing this and a solution.
