BECKHOFF C9900-P208 - Manual (Page 14)

Installation Instructions
12 C9900-P208 / C9900-P209
UPS output, C9900-P209 only
In order to maintain a screen display for the PC in the event of a power
failure, the C9900-P209 power supply unit is equipped with a UPS output
for connecting a Control Panel. The maximum load for the output is 1.4 A.
The UPS output is located on the power supply unit adjacent to the mains
plug (see also section
Product Description ).
UPS output function

The 27 V DC connection at the UPS output is live even after a power
failure. The maximum load is 1.4 A (C9900-P209 only).

Once the PC has been de-energized via the UPS software, the UPS
output is switched to 0 V. Any connected panel is thus switched off,
and total discharge of the rechargeable battery is prevented.