“A feedback circuit measures the output voltage and sends a signal to the controller IC, which adjusts the switching frequency to obtain the desired voltage.”
No.
It controls the “on” time of the switching transistor. Longer on time means that more charge goes into the capacitors on the output side, thus higher voltage. Conversely, shorter on time means less energy and therefor lower voltage at the output. The frequency stays the same. Think Pulse Width Modulated circuit.
But none of this has a damn thing to do with the subject. It’s just a couple of techie guys swingin’ our dicks around.
You are most correct. Does the frequency control the “on” time of the switching transistor; especially if the frequency is a square wave? I think so. This would point to the malfunction which could have applied a lethal current to the wet girl. I suspect the controller IC caused the charger to send out a high voltage when something caused to create an abnormally long “on” time. You don’t want such a malfunction to happen in an wet environment.
Back to the subject. What was cause of the electrocution due to a circuit failure, a circuit design flaw causing the non-isolation from the line voltage input, or a matter of the wet girl getting that lethal 7 milliamps current from a charger that was putting out more than 1 amp?
There is another matter. It was said that the cell phone charger was connected to an extension cord in the bathroom. That extension cords could have been plugged into an outlet without a ground fault interrupter. It could have been been plugged in with the polarity of the input voltage reversed, causing a hot ground plane. She was hit with sufficient current to burn her hand from the accident. This should be a warning not to charge a cell phone in a wet area.