Good advice from Ken...
Many people think they are putting 24V on all the devices on a network from a single power supply, but you have to consider the volt drop along the network, caused by resistances in the cable and the connectors - all are widely documented.
You have to make sure that all devices receive the minimum spec. voltage on the "red wire", so it's no good putting a second power supply on the network at the same location as the first, the volt drop will still ensure the distant devices may not receive the minimum voltage (19V, or thereabouts).
Most modern power supplies will happily "share" on a network, but the spec. for DeviceNet calls for segregation of the positive supply to the network when using multiple supplies. Do it by the book, and don't cut any corners, and you will have no problems.
There are network connectors that provide LED indicators of the supply volts at that point in the network, which is a great diagnostic tool, but is it worth the extra cost? Properly designed and installed networks have run perfectly, and unattended, for many many years.
Proper design and install are the key issues.