Capacitor For Inverter

NEVER connect a capacitor to any power electronic equipment's output side. The UPS or any other power electronic (inverting) equipment generates a PWM Wave only at its output. This is a series of DC Pulses - made to "look like" AC. In fact, they are fast transient DC Pulses and as such are rich in harmonics. Naturally, any capacitor connected at the output side of such equipment would offer a low impedance path for such harmonic currents and no surprise that your capacitor exploded. If you want PF improvement, connect capacitor at the input side of the UPS. Rather a series reactor on the input side would help.

In today's polluted network, all plain capacitors must be replaced with filter capacitors (at least de-tuned filters), because even if you are not generating harmonics, your capacitors can still 'import' harmonics from a neighbouring harmonic source connected to the same grid.

It shouldn't matter, though a Δ-connected capacitor bank needs a voltage rating √3 as much as a Y-connected one. If a capacitor has exploded, do not use the equipment until the suitability of the replacement and of the surviving capacitors has been verified.

A telephone call to the power factor correction unit's original manufacturer should be the first step.