Power Connectors

Often the question turned up if there is an adapter to supply older mainboards with an ATX power supply, or if there is an adapter to supply new mainboards with old AT power supplies. Both is either very problematic or simply not possible!

Old board with a new ATX power supply
In theory this would be possible, because the ATX power supply has all voltages, which are needed by the old AT mainboard. However, problematic is that the ATX power supplies only start up if the PWR-ON signal is set by the mainboard. This signal is not generated by an old mainboard. I.e. at this point you would need an additional circuit to generate it, which makes it impossible for most people. A second problem could occur by the fact that a big part of the power which an ATX power supply generates is on the 3.3V output. Therefore the 5V supply for these power supplies is designed much weaker. An old system does not need the 3.3V supply but uses a lot on the 5V supply. In some cases this can lead to problems.

New board with an old AT power supply
This combination is not possible. The new board needs a 3.3V supply which an old AT power supply is not able to supply. An adapter would have to include a voltage converter from 5V to 3.3V.

Conclusion
Somebody with enough knowledge of electronics could find a solution. This would mean a lot of effort and some danger for the mainboard. A commercial solution is not available, for none of the cases!