[0] Electronic noise at the input terminals [Linear power supply] Causes harmonic distortion to the input AC, but relatively little or no high frequency noise. [Notes] This can be prevented if a (properly earthed) EMI/RFI filter is connected between the input terminals and the bridge rectifier. [Switching power supply] 
Very low cost SMPS may couple electrical switching noise back onto the mains power line, causing interference with A/V equipment connected to the same phase. Non power-factor-corrected SMPSs also cause harmonic distortion.