I salvaged both of these parts and the one in the left has a schematic symbol that I've never seen before. I have spent hours trying to look up, but don't know what it is. The markings on it look like a date code for the first day of December 2009.
At first I thought it was a voltage regulator due to the three legs and TO-220 packaging. The markings say SE – B3 and the date code looks like 1D 09.
I put the lower right-hand voltage regulator in there, because I saw that black thing on the input voltage pin and thought it was to prevent arcing or maybe preventing a short circuit. But that is actually a ferrite bead on the leg of a voltage regulator if you can believe it. It's held on with heatsink goo and therefore likely dissipate some amount of heat. The voltage input must be coming from AC mains and the designer of the circuit was either low on space or cash, so that they didn't want to put any sort of other inductor to block the inrush current on the input voltage pin. So they use the tiniest ferrite bead ever made in the most ridiculous use I've seen a magnetic component used.
I cannot tell you what circuit I pulled it from. It could have been a closed circuit television so maybe a CRT. I took one of those apart not long ago but I've also taken apart hundreds of things that I find on the street, so who knows. I have thousands of three terminal TO-220 components that I can either read or identify the part number, so they are more like items for a museum than practical components.
Best Answer
That is an SE-B3 error amplifier.
I could not find an example circuit that uses it, or any document with more information than the linked datasheet.
It was most likely used as part of a voltage regulator.
Wikipedia has a section on error amplifiers.
This drawing from the wikipedia article gives a rough idea of how the SE-B3 could be used:
Lacking a better datasheet, I couldn't begin to guess which pin is what on that device.