Ripple flowing through probes connected to the same point!
Your two probe wires connected together at the "far end" (farthest away from the oscilloscope) form a loop antenna. They are picking up magnetic radiation from the transformer in the SMPS (Switch Mode Power Supply).

You could conduct a couple more experiments with the probes inter-connected but NOT connected to the SMPS.  And another experiment where you simply power down the SMPS and see what your scope shows without changing the connection.