Does polarity of scope probe matter when measuring ripple of the power supply module?
If your supply is floating, the inputs are reversible using the above methods.  However reversing the leads may conduct some ACDC supply filter noise current (0.5mA) if output is earth grounded.

Test Engineering Methods for measuring DC supply ripple.






simulate this circuit &ndash; Schematic created using CircuitLab

For quick and easy setup, use a BNC "T" connector on DSO with a small R 1/4W termination inserted in one port only with a 1:1 probe or coax BNC connector in the other port.

Using a short probe and ground leads reduces the effects of false ripple measurements from load induced CM radiated noise and stray coupling.  

This occurs due to inductive noise pickup of 10:1 probe ground and ~>=20MHz resonant frequency of probe ground wire inductance and coax capacitance.

If you do not have an expensive FET buffered TEK Diff. probes, this is the next best option with scope preset to AC coupled.