The problem with the capacitors is not that they dry out, but that the liquid electrolyte in the capacitors heats up due to the electrolyte conducting ac ripple current and heating, eventually blowing the electrolyte out through the overpressure vent, (the radial frangible lines on the end of the capacitor).
The "goodness" or ESR (equivalent series resistance), of the capacitor can vary with age and ambient temperature, normally upwards. The heating effect is Watts = (Iripple) squared x ESR , or the heating effect is directly proportional to the value of the ESR.
READ :- http://wiki.xtronics.com/index.php/Capacitors_and_ESRThis is a mains switching power supply. It can give you a nasty shock. MAINS IS CONNECTED DIRECTLY TO THE CAPACITOR WITH NO SAFETY ISOLATION. Please make sure that the PS is disconnected from the mains and the caps are discharged BEFORE you work on the supply.
The capacitors in the Sheevaplug V 1.3 ( second generation) 's power supply:-
The problem capacitor is the mains full wave rectifier smoothing cap. Fitted as standard is a general purpose 400V 6.8 ufd 105 deg C aluminium electrolytic. I would recommend fitting a special purpose power supply filter capacitor with defined LOW ESR, 400V 6.8ufd 125 deg C aluminium electrolytic.
Also worth changing is the "snubber" capacitor, a 400v 22 ufd 105 deg C capacitor. Again I would replace this with a special purpose power supply filter capacitor 400v 22 ufd 125 Deg C LOW ESR part.
The 125 deg C parts will also give you a bit more margin.
You will have to find a supplier of good quality power supply filter capacitors. Places like Maplins will sell you general purpose capacitors, that will be no better than the ones already fitted.Once again I must reiterate, if you are not trained to work on hazardous mains power supplies, then get someone who is competent to do it for you!