PC Power & Cooling are no more. Well, not really anyway. They're owned by OCZ now, since 2007. The Silencer Mk.II line are just overpriced modified OCZ Z-series PSUs from Sirtec, not worth it at all usually.
However, they recently re-released the Silencer 910W, and introduced a new model, the Silencer 760W, which are SeaSonic S12D units (non-modular version of M12D, same thing as the XFX BE 850W). So maybe OCZ decided to respect the community a little and not foist overpriced rebrands on us. Though the new Silencers are still probably going to be overpriced.
Corsair rebrands SeaSonic and CWT (and Flextronics, for the AX1200). Their only units that are really "outstanding" are the HX750 and HX850 (CWT DSG units), the AX750 and AX850 (SeaSonic X), and the AX1200. The rest of their lineup ranges from low-end (CX) to midrange (TX, other HX).
XFX uses all SeaSonic. The XFX XXX 650W is a sort of a kludge, a modification of the PC Power & Cooling Silencer 610W (which was in itself a minor derivation of the SeaSonic S12 650W). When OCZ gave SeaSonic the finger back in 2008 (or vice versa; it's unclear) SeaSonic had a bunch of extra Silencer 610W PCBs lying around (apparently they were making a new batch of those at the time), and suddenly they couldn't do anything with them. So they talked with XFX, and they came up with a modified version based on those PCBs (with the PC Power & Cooling logo marked out with black marker). I'm not sure why they modified it really, because now it has problems with crossloading and low +12V loads, and the fan they picked is really cheap. So the XFX XXX 650W is just ok at best.
But the XFX Black Edition PSUs are SeaSonic M12D units and are top notch, comparable to the Corsair HX750 and HX850. The XFX Pro PSUs are a custom SeaSonic platform, they look like a mix between S12II and S12D, and perform somewhere between the two.