If the TI 58-c is the same or similar to the old TI-58 which was the same as the TI-59 but without the card reader and half the memory, then it is TI Model AC-9131, 3.3VAC 500mA. In other words, the above AC adapter is for a TI-59 ca. 1979. It shouldn't matter which way it's connected, because it is an AC adapter. Inside the battery compartment of the TI-59 you can see the four diodes of the bridge rectifier. Jeff Walther