An RF amplifier does not have one universal acceptable ripple value. Specify rail noise versus frequency, measurement bandwidth and probe method, then relate it to allowable carrier spurs, AM noise or phase noise at the relevant frequency, output level, bias and modulation state. A millivolt RMS figure without spectrum and test conditions cannot be applied safely.
Reject a regulator or filter when switching fundamentals, harmonics, beat products, burst-mode transitions or low-frequency noise exceed the allocated RF contribution, even if total RMS ripple looks small. Where risk is material, inject known rail modulation or compare controlled supplies to characterize the supply-to-RF transfer, then retain margin for layout, grounding and unit variation.
Provide the RF limit, offset-frequency range, rail, bias point, load state, regulator mode, filter, grounding and measurement setup. LDO post-regulation can lower noise but adds heat; switching conversion can reduce dissipation but needs verified filtering and stability. Selection is a measured tradeoff, not an automatic preference for either topology.