I've provided solar power for the last few summer field days.  We had already noticed the 120v inverter was generating unacceptably high interference on our radios, but this last event we also realized the solar controller was generating interference, and that one wasn't really optional so we needed to find a way to filter our power  This sort of interference is going to come from any switching power supply, inverter, power converter, or even other accessories generating "noise" (EMI) on the same power line.

I've been assembling a variety of of different filters to test (as well as purchasing a few fully-assembled units) to see what works the best.  Unfortunately, EMI can come in many forms, and one filter can't protect you from everything, so it's good to have options so you can go with what works for your specific EMI problem.  In my tests however, this specific filter worked extremely well for any interference coming over the power wires.  This was a 12 volt DC power, but this filter works equally well for 110VAC also.  (the capacitors are rated 310 and 400 volts, so 220 should be fine also, but don't try 440, and it won't work with 3-phase)

I tested several filters, including a professional CUI, using a large battery as the power source, with a 120VAC true sine wave inverter powering a 750w ceramic heater as a source of EMI.  As soon as the inverter was turned on, the radio receiver (IC-7300) powered from the same battery immediately showed significant interference on 40m/80m, with regularly spaced S-5 spikes on the waterfall.  These spikes went well over S-9 when the heater was turned on, loading down the inverter and amplifying the interference it was producing.  For those not familiar with radio, this level of interference made it almost impossible to hear what was being received.

This filter and the CUI both were able to remove the unloaded noise, but when the load was turned on, S-5 spikes appeared through the CUI.  This filter however, was able to completely remove the loaded spikes from the waterfall, leaving a totally-acceptable faintly-audible sound at the exact points of interference.  I attribute this extremely effective performance on this filter being a two-stage common-mode filter.  The CUI I was comparing it with used a single stage common-mode, followed by a high-side differential mode. (just a choke in series)  The CUI did better when I placed a second one in series with it, but THIS filter can clean up even strong interference in one shot.

Just to clarify for the seller, the picture in the listing includes a shot of the 25 amp filter, with the 15 amp filter below it.  You only get the one you order.  They should update the listing so that the image changes to just one board or the other when the buyer selects which board they want.

Also, you don't really need a manual, since it's a "plug it in and it works" sort of thing.  Grounding is optional but is likely to help if the interference is much higher frequency or RF noise ON the frequency you are trying to receive.  (I suspect most people considering this filter are dealing purely with power line EMI and so connecting the ground won't help them much if at all)  The ground connection is in the middle on both sides, and the outer two contacts are for your Live/Neutral or +/- power connections.  Live/Neutral or +/- can go to either connection, the circuit is symmetrical and not polarized.  Either end of the board works equally well as input or output.

Though if you're not able to figure this out on your own, you probably shouldn't be ordering this product for 120VAC filtering, as I question you can safely handle or install it.  This isn't a consumer-packaged part you can just leave plugged in laying in the living room with the kids.  It's a component, with exposed live contacts, and requires competent installation to be used safely.  If you're planning to use this for 110vac or higher, don't try it if you don't feel comfortable replacing an AC outlet.   If you're going to use it for 12VDC like me though, its quite a bit safer, though when dealing with any sort of power you can still start a fire if you misuse it.

I've purchased a total of four of the 25 amp boards.  All were identical, with clean assembly, good solder joints, and quality components.  The boards were shipped in adequate bubble wrap via UPS.  I couldn't ask for better.  I'm recommending this board to all my friends that are having problems with EMI on their radios in their home or in their car.