just met an industrial computer which has the following power adapter jack. how to identify this jack and where to find? (actually there are lots of different jacks here and there, how to identify all!).
Others have identified the power connector as a Kycon 4 pin:
It's not extremely common like coaxial dc barrel jack connectors, but common enough. Provide for higher Amp rating than the smaller barrel jack connectors. As I noted, your pc uses 5 Amps at 12v. I've seen these connectors on LCD monitors, thin clients/embedded pcs and small Stereos.
While the label for the connector is shown as a typical barrel jack label (Center positive), that is not correct for this connector. Any of the four pins can be V+ or Ground, or any combination of it. My thin client used 12v on the top two, and Gnd on the bottom two pins. Some thin clients use the same connector for 5v, so you need to be sure which ever adaptor you get matches the wiring needed, or you will need to rewire it. The label makes me believe that the same case is used for a number of the manufacturer's offerings, some requiring less current, thus a barrel jack connection.
As for finding the adaptor, and identifying the other ports on that embedded pc, you will be best off googling the brand and model number of the pc. Or of the motherboard inside if it has no outward branding. Most other jacks on that pc should be standard ports, ex: USB, Parallel, Serial, VGA, DVI, PS/2, Audio, etc.
The top-right blue connector looks like a VGA display connector.
The power connector is a non-standard variation of the mini-DIN connectors. It's a Kycon 4-pin DC power connector.