How to output an amplitude of 10 volts PWM signal?
I don't know if this is the only problem with your circuit, but the trigger threshold (assuming a bipolar 555 like LM555) is 1/3 of VCC (Actually lower and variable due to your connections to CON, thanks to @Jasen for pointing this out).
If you increase VCC without changing the amplitude of the trigger input, eventually the trigger input will never go low enough (because you are ac-coupling and re-biasing to Vcc) to be registered as &quot;low&quot; and the 555 will never see low-to-high transitions of the trigger.