Although necessary, determining that EMI emissions meet EN or FCC limits isn't always sufficient. Sometimes, emissions that meet specified limits still interfere with nearby sensitive equipment. Generally speaking, resistive loads are the most benign in their treatment of ac lines. Except when you first switch them on, loads such as incandescent lights, toasters, and electric heaters, draw sinusoidal currents that are in phase with the line voltage. The transient current diminishes as the load approaches its steady-state operating temperature.
Electronic equipment presents loads that, quite often, are less well behaved.
The majority of such equipment uses power supplies in which capacitor-input filters follow rectifiers. This statement is true whether the supplies use linear or switching regulators. In linear supplies, the rectifiers and filters normally appear in the power transformer's secondary circuit. The power transformer, which appears later in the circuit, operates on the switching regulator's high-frequency output. Additional rectifiers and filters in the transformer's secondary circuit convert the transformer output to dc.