I have several Linux servers connected to APC UPSs. They are connected to the UPS via USB and configured to shutdown if the UPS sends a signal that mains power has been lost and has not returned after a period of time. This works well. In addition they are configured via jumpers to automatically power on if power is lost and then returns. This also works well.

The scenario that is causing issues is when mains power is lost, and the server shuts down, but then mains power is restored before the UPS runs out. In that case we'd like the Server to start up again, but since power is never actually lost post-UPS, the server never sees a power-return event and therefore doesn't power on.

I'm hoping there exists a device that can plug into mains power pre-UPS, and sense the power return state and send wake up signals perhaps via Wake-on-Lan to preconfigured servers to wake them up once mains power has returned that someone can point me to.

Alternate suggestions are also appreciated, only thing I can't do is replace the server hardware, and I'd prefer to keep the same UPSs if possible.