OBDII cables are usually more than just cables. They all have an OBDII connector on one end and either a USB or serial connector on the other. Most of these cables include basic electronics to convert the OBDII hardware interface for use with, and to electronically protect, the computer to which it connects. Other cables are more rudamentary and rely on being connected to other electronic modules which must take care of the interface (and protection) to the computer.
This page attempts to capture the various options available including details of how to build your own cable and electronics if you are to inclined. The author has no affiliation to any commercial product described here however recommends the use of them as a safety precaution and especially a tried and tested solution.
OpenPort OBDII Cable
OpenPort 1.2 OBDII cable from Tactrix in the USA is around $79 (£45). This cable is compatible with various Subaru ECU diagnostics, reading, editing and reflashing OpenSource software described on this site. Connecting up using this cable is described in more detail in the connecting to your ECU technical article.
OpenPort OBDII Cable Solution