Some people seem to think that "reforming" an aluminum electrolytic capacitor is some kind of cheat, akin to zapping NiCd cells or rejuvenating CRTs. Actually reforming is the same electrochemical process that the manufacturer uses to "form" the capacitor in the first place, building up the aluminum oxide layer, before the sheet is rolled into cylindrical form. The manufacturer typically uses a forming voltage higher than the rated voltage, from 135% to 200%, to provide margin for shelf life. When the capacitor goes unused for an extended time (shelf life), the oxide layer gradually breaks down, increasing the capacitor's leakage current and reducing the effective usable voltage of the capacitor, which is proportional to the minimum oxide thickness. If the oxide has developed spots that are too thin for the applied voltage, it may be damaged ("punch-through") when that voltage is applied. Punch-through tends to be a runaway process, so even a small amount of punch-through usually completely ruins the capacitor. Reforming the capacitor by applying current-limited power rebuilds the oxide layer to prevent this type of damage, and to reduce the leakage current back to within the specifications. The current limiting is what prevents the reformation process from causing punch-through and damaging the capacitor. Many of the capacitor vendors actually publish recommendations for reforming their capacitors. See for example information on manufacture on pages 13-14 and a brief recommendation of reforming procedure on page of 17 of Kemet publication F3304 dated June 2009: http://www.kemet.com/ProductCatalog%20Documents/F3304.pdf Also pages 2-4 on manufacture and page 16 on "recondition" (reform) of "CDE Aluminum Electrolytic Capacitor Application Guide": http://www.cde.com/resources/catalogs/AEappGUIDE.pdf Also pages 1-5 of Nichicon "General Description of Aluminum Electrolytic Capacitors": http://www.nichicon.co.jp/english/products/pdf/aluminum.pdf In at least some aluminum electrolytic capacitor manufacturing processes, there is actually a reforming step done after assembly, in addition to the initial forming. See page 9 of the Panasonic "Aluminum Electrolytic Capacitors Technical Guide", dated April 2013: http://industrial.panasonic.com/lecs/jp/i/29880/TAL_E/TAL_E.pdf The reforming process WILL NOT fix other things that may go wrong with the capacitor, such as failed seals allowing the electrolyte to dry out, or corrosion, or punch through which can result if the oxide layer is degraded and voltage is applied without current-limiting. The US DoD published a technical handbook detailing their policies and procedures for reforming aluminum electrolytic capacitors that sit in inventory for years, MIL-HDBK-1131. As of 1999 this is "for guidance only and should not be cited as a requirement, but the information in the handbook may be useful in determining or evaluating requirements." For non-mil-spec capacitors, it recommends inspection and possible reformation every 3-6 years of shelf storage. It recommends disposal after 12 years of shelf storage, but AFAICT they're just being conservative, possibly due in part to not having enough practical experience with reforming very old capacitors. Shelf storage is of course equivalent to having the capacitor in-circuit but unpowered. Having the capacitor powered in circuit for any significant length of time will reform the oxide to some extent based on the applied voltage, though not up to original factory spec. When I reform capacitors myself, I use a reforming voltage of 135% of the rated voltage. Since I use a suitably low current limit, this has no significant probability of damaging the capacitor, but as with the initial factory forming, provides some margin for further shelf life. In my experience, aluminum electrolytic capacitors in equipment that has been unpowered for 30 years or more almost always need reformation, but they almost always meet factory specs (capacitance, ESR, and leakage at rated voltage) after reformation. Since I don't tend to restore equipment newer than that, I don't have any empirical data on how much shelf life they can have without needing reformation. I'm not particularly advocating for or against reformation, as compared to replacement. Anyone restoring equipment with electrolytic capacitors is advised to to read the references and decide for themselves. Eric