A major problem is Switch Mode Power Supplies (SMPS) the small power packs that charge cell phones and computers; previously these were 50 Hz transformer-based with associated rectifiers. The latter were heavy due to the iron core. The SMPS uses a LF oscillator, a lightweight transformer and rectifier. A well-designed unit with adequate output filtering can be satisfactory, but occasionally a manufacturer, after the designer has acquired the required technical approval for the unit, will leave out filtering components to save costs of a dollar or so in the production phase. This is a small amount, but over a production run of several millions resulting in an acceptable profit.