Prevalent on ebay and Amazon is the "LTC3780 Automatic lifting pressure constant voltage step up step down 10A 130W" DC to DC Converter.
I'm not quite sure what the "Automatic lifting pressure" is about, but it is a fairly well designed DC-DC switcher based on Linear's LTC3780 - High Efficiency, Synchronous, 4-Switch Buck-Boost Controller. It sells for about $20 to $25 USD.
My interest in this DC-DC switcher is to operate 19VDC Laptops/notebooks and LCD TVs from 12V batteries/solar.
I took the plunge and purchased two units. Here are the specs:
You will notice there are three trimpots and an absence of documentation. Well that's not quite true, I did find the product datasheet if you can read Chinese.
Upon delivery, it was evident one unit was touched up on the production line. There was evidence of flux around the LTC3780, and in the process of touching up the joints, one of the trimpots were burnt.
Pushing ahead, the next task was to connect the converters to a bench power supply and DC load and put it through their paces.
During testing of the adjustable current limiting, I fried one of the boards. No output, just the red fault LED steadily illuminated.
The next stage was to investigate the cause. In doing so, I sketched out the following schematics of the supervisory aspects of the DC-DC switcher.
The low voltage disconnect and adjustable current limit is controlled by a commodity LM358 Dual Operational Amplifier running from 5 volts. This 5 volt rail is generated by a LM7805 linear regulator.
The red Fault LED is connected to the LTC3780 power good (PG) output.