by Ilija Uzelac @ edn.com:
This Design Idea presents a simple, proven, reliable, and robust method for charging large capacitor banks, using a series connection of power MOSFETs to raise the breakdown voltage over that of an individual MOSFET.
When a power supply drives a large capacitive load, inrush current, if not limited, can reach tens or hundreds of amps for a high voltage power supply. In general, maximal ratings of a power supply could be transiently exceeded by many times, but this is generally acceptable when the transient lasts a few AC-line cycles. This is typical for load capacitances up to a couple of hundred microfarads, but for load capacitances in thousands of microfarads, an inrush current limiter is a must.
Series-connected MOSFETs increase voltage & power handling – [Link]