I am working on an application that requires isolated power inputs.
Wondering if the standard ATX PSU has any isolated outputs?
Why are we having multiple ground pins on the Connector?
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The outputs of the ATX power supply are isolated from the mains. The outputs of the ATX power supply are not isolated from each-other. In other words, +5V and +12V output "share" the same ground.
Multiple ground pins increase current carrying capacity. I bet, you will see continuity between them if you check with a meter.
My information comes from several ATX power supply reference designs that can be found on the web (such as this one). Such reference designs contain detailed schematics. A complete schematic would be a bit too detailed for the purposes of this conversation. But here's a block diagram.
Per this link, the ATX provides isolation from the wall power supply. But their outputs share a common, the link also gives the simplified circuit of a PC PSU.
And the ATX standard defined the connector pin-out. There are many "COM"s on a connector, beside the reason for interconnecting, there are reasons to increasing the current carrying capability. Because connectors usually has a rated current carrying per contact, if your output current greater than this, you need more contacts.