I've even seen, some of them blowing up.
One of them even had a capacitor that was under rated (4.7v) at output.
Many of them don't fit any country's socket thus keep sparking away ruining itself overtime.
And about y caps making screens go haywire. Chinese chargers do make my moto defy's screen nonfunctional when charging. But my galaxy s4, moto z, and chinese phones still function well while charging.