Several points: 1. do not confuse time domain linear scale with frequency domain logarithmic scale. 2. time domain signal is a composite of the frequency domain components - it is necessary to include all the harmonics to arrive at the correct time domain amplitude. 3. there is a 60 Hz amplitude modulation evident on the SMPS as well as many other harmonics. The ripple is not a simple 500 Hz sine wave. See examples below. 4. The period of the Jay's audio signal is consistent with that of a 60 Hz sine but is also a complex waveform, not a simple 60 Hz sine. See examples below. 5. Zoom the U8001A picture to see the 60 Hz noise. The difference between the Jay's audio 3 mVpp ripple and the Keysight U8001A 670 uVpp ripple is 13 dB total. The waveforms look considerably different. Keep that in mind while going through the examples below. Some examples using a signal generator with sine and arbitrary waveform output. These will be clean, without high frequency noise, for visual clarity. 60 Hz 200 uVpp ripple - time domain Looks like a sinusoid. 60 Hz + multiple odd harmonics 800 uVpp amplitude - time domain Has a period consistent with that for a 60 Hz sinusoid but doesn't look like a 60 Hz sinusoid. Note the 12 dB amplitude difference between the two time domain examples. 60 Hz 200 uVpp ripple - frequency domain 60 Hz + multiple odd harmonics 800 uVpp amplitude - frequency domain Note that both frequency domain examples have the same -82 dBu 60 Hz component. SMPS 4 mVpp ripple Note the amplitude modulation and also the thickness of the traces. Amplitude modulation are mains noise. Thickness of traces indicate noise in the spectrum. While the trace does have similarity to a simple sine, this is still a complex waveform which when converted to the frequency domain will have plenty of components other than the obvious one at 500 Hz. Keep in mind the previous example demonstrating a 12 dB difference in time domain amplitude while having the same 60 Hz frequency domain component.