I had an old slot 1 Compaq built PC in storage that I recently was trying to put to use. The board would power up but not post. No beep codes or anything. I tried swapping, RAM, reseating CPU, and then decided to try a different PSU.
I plugged in my test PSU, and immediately upon applying AC to the PSU, I heard it make a *zip* noise which indicates that its overcurrent protection had been tripped. After some troubleshooting I discovered that the PSU in the original Compaq case was using a non-standard pinout

. The ATX connector was keyed identical to a standard one and I did check a few of the wires to make sure before plugging the new PSU in, but it turns out the Compaq PSU only 90% conforms to the standard ATX pinout. There were a couple wires that weren't standard.
Most notably, the Compaq PSU has a 3.3V standby wire where the standard ATX supply has +12V... Upon plugging the Compaq supply back in, the board would no longer power up. I traced it to a short on the 3.3V standby pin that received the 12V. Providing the 3.3V rail with my lab power supply draws 500mA and the southbridge chip gets hot.
I have the equipment required to replace the southbridge, but I have two questions. What is the likelihood that every other chip on the board is destroyed as well? Or is it possible the southbridge died first, and overloaded the PSU protecting the other components?
The southbridge is an Intel FW82801AA. (See attached image) However, it also has the markings SL3MA on the third line. Most replacements I can find online seem to have SL5WK marking on the third line. I did find one used chip with the correct SL3MA marking. The full Intel datasheet is available online, but it does not describe the package labeling information.
Would any FW82801AA chip be likely to work, or would it be necessary to buy the SL3MA marked part?