Capacitors connected in parallel add together their respective capacitance algebraically. This means these two capacitors when connected in series can safely operate with a 500 Volt potential across them. The main capacitor has a working Voltage Rating. This is the working potential it is designed to operate in. The higher the working voltage, the more electrical energy the capacitor can store as work without being destroyed.
Energy goes up as a square of the voltage .
It also goes DOWN as a square of the voltage. Still quite respectable. This gives us potential to do work. But the coil needs Amps to make Gauss . With all else being equal, the higher the Volts , the higher the Current and the higher the Gauss .