Switch port to standby and then back. Unfortunetly unless you are running 3560E switches there is no way to do this which is less than ideal . Whats the point if you have to manually change the rps back , the same issue exists with their other switches like the 2960 also . I would think they could incorporate this feature into the IOS code if they want people to buy these rps's . Here is the explanation out of a doc.
Q. Why does a device continue to draw power from the RPS even after its internal power is restored?
A. This is expected behaviour for all devices, other than the Catalyst E series switches. The device might reboot when reverting back to its own power supply. Hence, it continues to draw power from the RPS, so that the device can be switched back to its own power supply at a convenient time. In order to switch the device back to its own power supply, place the RPS port in "Standby" mode until the device reverts back to its own power supply, then place the RPS port in "Active" mode again. The Catalyst E Series switches are capable of reverting back to their own power supplies without service interruption.
