I am using the rb2011 series routers and CRS125-24G-1S-RM switches. Can these be powered at the same time by the POE in and the DC power jack? Sort of as redundant power?
I’m not going to try it and fry one if it went wrong 
so I’ll ask.
Hi,
I believe you can use both the DC and the POE inputs. The board will use the higher of the voltages and automagically failover to the other when the primary fails.
There is a MUM presentation on this somewhere.
Regards, Dave.
I have done this on RB2011, but will it work on RB450G ?
According to the guide here: http://i.mt.lv/routerboard/files/rb450G-qg_1377089382.pdf
Powering
The device accepts powering from either of the two power jacks, or from the LAN1 Ethernet port:
•
direct-‐input power jacks J801/J803(5.5mm outside and 2mm inside diameter, female, pin positive plug) accept 8-‐30V DC (overvoltage protection starts at 30V).
•LAN1 Ethernet port J504 accepts 8-‐30V DC input (at the board;higher voltage needed to compensate for power loss on long cables) from non-‐standard (passive) Power over Ethernet injectors. The board does not work with IEEE802.3af compliant 48V power injectors.CAUTION: all three power inputs are always active, but only one of them may be used at time to avoid damage of equipment.
As you can see, the document states that ONLY ONE power input can be used at a time, so the use of both DC and POE does not seem possible.
Can anyone confirm the use of this dual power solution during extended periods of time?
Thanks!