useful tool

I've found these pretty handy:



https://www.amazon.com/20pcs-10pairs-Female-Adapter-Connector/dp/B018YQF9M0/ref=sr_1_10?ie=UTF8&qid=1484511673&sr=8-10&keywords=2.1+5.5+jack

You can connect a lot of bi-pin track light bulbs to the screw terminals, so it's an easy way to make 12-volt DC lighting. I've tried G6-sized halogens up to 35 watts and G4 sized LEDs. The 35W halogen got hotter than I like, but 20W was no problem.

On the other end of a DC extension cord, I've tried two different types of power filters:

The first one uses the same connectors to splice a pair of inductors between the cord and a 12V power supply. I used these:

https://www.amazon.com/Haobase-Ferrite-Toroid-Inductor-38mOhm/dp/B01LAH7VFI/ref=sr_1_1?ie=UTF8&qid=1484513917&sr=8-1&keywords=haobase+toroid+inductors

They were so-so, so I ended up buying some with high inductance (filtering ability).

https://www.amazon.com/gp/product/B01LBO71X2/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 (very slow shipping)
https://www.amazon.com/gp/product/B00EZC70M0/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B00EZC7CK0/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

I unwind 1 or 2 loops from each end of the inductors to make it easier to attach them, and then use some heat-shrink tubing or electrical tape for insulation. You can daisy-chain them to increase the degree of filtering.

The more effective type uses a Texas Instruments linear regulator (also called an LDO) instead of inductors. I bought them on Amazon, but they were over-priced:

https://www.amazon.com/INSTRUMENTS-TL780-12KCS-LINEAR-REGULATOR-220-3/dp/B00LQOHTJY/ref=sr_1_1?ie=UTF8&qid=1484512507&sr=8-1&keywords=12+volt+linear+regulator+texas

Mouser is a better source:

http://www.mouser.com/ProductDetail/Texas-Instruments/TL780-12KCS/?qs=%2fha2pyFadugnGoBlyl9tMKwqiLheqOikvtPhtUd20Z4%3d

You can get them in a variety of voltages, and there are other brands as well:  http://www.mouser.com/ProductDetail/STMicroelectronics/L7812CV/?qs=5Uvc6lfWVJzVGZQZmBynyg%3D%3D - also available on Amazon, but over-priced

They worked for me on the first try, but I'm not 100% sure that I wired them correctly.

Datasheets for both 12V regulators:

http://www.ti.com/lit/ds/symlink/tl780-12.pdf
http://www.mouser.com/ds/2/389/l78-974043.pdf

I think that the top side mentioned in the Texas Instruments datasheet ("TOP VIEW") is the side with the TI logo and model number (TL 780-12), since that's how they're installed in circuit boards. The middle pin on the STMicroelectronics regulator is labeled as GROUND in their datasheet, and the TI datasheet calls the middle pin on theirs COMMON. I treat it as a ground, but I'm not if that's correct. It seems to work.

Assuming that the labeled side of the TI regulator corresponds to the top view in their datasheet, I connected the INPUT pin to the positive screw terminal on the female jack that connects to the power supply. Then I connected the OUTPUT to the positive terminal on the male jack that connects to the extension cord. Finally, I used some spare insulated wire to connect the negative terminals together and close the loop.

Regardless of how you connect regulators, you need to bend the pins to make them fit, but that's how they're normally installed on circuit boards. The only difference is that I left the middle pin unbent and bent the others in opposite directions so that each one would fit into the corresponding DC jack.

The other limitation is that both of the regulators above are limited to 1.5 amps (so you can't use a 20W halogen with this filter, although it works fine with the inductors).

The best G4 LEDs that I've tried so far don't work very well with the TI regulator for some reason, but they're nice otherwise:

https://www.amazon.com/gp/product/B00NTTJCZS/ref=oh_aui_detailpage_o04_s01?ie=UTF8&psc=1

The halogens that I've tried are old ones that I had lying around, but they're similar to this:

https://www.amazon.com/Westinghouse-0478100-Hours-Halogen-Light/dp/B00FB0EY10/ref=sr_1_1?s=hi&ie=UTF8&qid=1484516570&sr=1-1&keywords=12v+halogen&refinements=p_89%3AWestinghouse