a little more detail. the x means it uses Class X flame retardant dialectic -- in Germany for sure and probably most the eu, class X dialectic is required if you add filtering. any filter cap that goes between the mains and neutral had be made of class X (or class Y if my memory serves me) material or you can't getter German equiv of the us UL for the device [google this if you want to understand more]. that said, the other thing you will see across mains for safety is a semi-conductor called an MOV (metal oxides varister). it has two pins and looks like a cap often orange red or blue and very glossy material but I would not bet on the color. if the designers of the ps assumed an MOV i'd make sure you replace with that not a filter cap. On Sep 28, 2013, at 4:45 PM, Hans Vlems <hvlems at zonnet.nl> wrote: Thanks Dave Van: Dave McGuire Verzonden: zaterdag 28 september 2013 21:23 Aan: hecnet at Update.UU.SE Beantwoorden: hecnet at Update.UU.SE Onderwerp: Re: [HECnet] Alpha Server 1200 p/s schematics It's a capacitor that is rated to be placed across (hence 'X') the AC line. They are usually applied in just that situation, and are basically for filtration. However, their secondary purpose is as a "sacrificial" component to protect the rest of the power supply in the event of a large differential glitch between the two AC lines. One must never place a "regular" (i.e., non-X-rated) capacitor in place of one, though. Capacitors designed for such duty are usually physically marked with an 'X'. -Dave On 09/28/2013 02:49 PM, Hans Vlems wrote: -- Dave McGuire, AK4HZ New Kensington, PA