[Linear power supply] Causes harmonic distortion to the input AC, but relatively little or no high frequency noise. [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. [Notes] This can be prevented if a (properly earthed) EMI/RFI filter is connected between the input terminals and the bridge rectifier. [0] 
Electronic noise at the input terminals