I learned that the higher voltage on the cap always should be on the + else it is bad and you have to replace the cap.
If the cap is still full and both + and - are disconnedted, how does the cap know it is higher then the - ?
How can i explain ?
A capacitor holds charge. The polarity of that charge is determined by the circuit that it is placed in. If you remove the power input to your circuit, the capacitor will
not become "confused". The charge polarity will remain the same as it was the moment power was disconnected, and it will discharge to zero at a rate determined by the load it is attached to (as well as it's own leakage). Think of it like a battery. When you have a battery that is not in a circuit, it does not need to "know" which side is positive or negative. Conversely, many devices do not have an on/off switch, such as power supply "bricks" for laptops and phones. When you unplug these devices, the DC filter capacitors drain through the circuit that is loading them. Hope that helps!