What will happen if a PoE powered patch cable is plugged into a normal RJ-45 plug?
Solution 1:
The PSE (Power Sourcing Equipment) and PD (Powered Device) negotiate to see if the end device is compatible of being powered and at what standard. So plugging in a non PoE device will not damage said device.
Here is a good read about the basics of PoE (Do note though the document is quite old and was written prior to the 802.3at enhancement which modifies many of the issues covered.)