TBI, maker of Magellan subs and Millenia amps, created this reservoir/scrubber to overcome many of the shortcomings in outboard SMPSs up to 24 VDC. I can attest it offers many of the benefits of a high quality linear PS at a much lower cost. These are no longer made, but are an amazing product, IMO.
Just take the output from the outboard SMPS for your amp or PC and run it into this 4x6x2" device and back into the device as normal. It needs no other power. It uses the standard one pin connectors as is commonly found on such devices on the input and the umbilical output.
Designed originally for Millienia amps, but I've used it for abut a year with a small HTPC and it is a nice improvement over the stock SMPS alone.
Info:
http://www.tbisound.com/_pdf/UPFAwp.pdf I'll pay shipping to the cont. US at my price.
Thanks for having a look. You won't see many of these!
