I can't give a highly technical description, but there appear to be at least 2 ways to do Power Factor Correction. It is my understanding that in a passive unit, a network of fast capacitors creates a reservoir or buffer of steady AC current capacity available to the equipment downstream. This is expected to yield greater dynamic range, detail, etc. . . Furman Audio has taken this route with its products and combines PFC with an isolation transformer to pre-clean the incoming AC. I have not used Furman products so I cannot comment on audible results. However I have just spoken to a Furman engineer and his explanation of Furman product appeared to be very solidly based on principles of electrical engineering and NOT in New Age techno babble.
A more radical approach appears to be the PFC designs of Jeff Rowland Design built into the 300 series amps, the Continuum 500 integrated, and recently in the external dedicated PC1 unit compatible with some of JRDG other products. The JRDG design adds the general principle describe above with the conversion of universal voltage AC into a 385V DC current. If an amp or pre can accept such a current, its own internal capacitors are expected to be always kept at an ideal state of charge, because they will not be affected by any 50hz or 60Hz rippling of the AC. I have applied a PC1 on a Capri, and admit the audible benefit is significant.
Furman suspects that, at least in principle, current rectification combined with capacitive PFC may introduce an undesirable rise in impedance. I do not know how JRDG addresses this potential issue in its PFC designs, but I have not yet perceived audible problems in the Capri+PC1 combination. If anyone knows what the audible tell-tale of a rising impedance problem may be, please post here so I can try to detect it.
The only word of caution I have is that you should connect an active/rectifying PFC device like the Rowland PC1 only to a component capable of handling 385V of DC current. Check with your manufacturer before any experiments, unless you are a real fan of in-home sparklers and fireworks replete with 'sight&sounds&smells.' Passive PFC's like the Furman can instead be applied to any component.
