Series Electrolitic Cap life
The circuit in question looks like this:







simulate this circuit &ndash; Schematic created using CircuitLab

When the switch is open for 230 VAC operation, the four diodes work as a bridge rectifier, putting pulses of current into both capacitors at 2&times; the line frequency.

When the switch is closed for 120 VAC operation, D3 and D4 never conduct, and D1 and D2 function as a voltage doubler. C1 and C2 are charged separately on opposite half-cycles of the AC input, and each one sees pulses at 1&times; the line frequency.

What this means is that in the latter configuration, the ripple current for each capacitor is twice as high. Ripple current is the primary contributor to internal heating in an electrolytic capacitor, and heat is the primary limitation on electrolytic capacitor life. The heating effect is proportional to the square of the current, so even though the pulses occur half as often, you still get twice the heat.