Can´t give you the value for no connected ports; but I measure around 40W (on 220V/50Hz power) with 5 ports and 18W PoE draw:
(ArubaS1500-12P) #show poe controller
Linecard Power Budget(W) Power Consumption(W) GuardBand(mW) PoE Management Cisco Compatibility Config Delay(ms)
-------- --------------- -------------------- ------------- -------------- ------------------- ----------------
0 120 18 11000 Dynamic Disabled 2000
Earlier, I had three more PoE devices connected total 45W; then the device draw 72W:
Linecard Power Budget(W) Power Consumption(W) GuardBand(mW) PoE Management Cisco Compatibility Config Delay(ms)
-------- --------------- -------------------- ------------- -------------- ------------------- ----------------
0 120 45 11000 Dynamic Disabled 2000
See the graph below, the blue line shows the power consumption in Watts, and drops from 72W to 42W after I pulled 27W of PoE devices in the right of the graph (just before 8PM):
Unfortunately, I can´t pull the last device as that is a 7005 controller running my network. I would at least expect another 18W drop if you take off the last 18W of PoE powered devices.
The device measuring the power is a Plugwise power plug with just the cable to the switch direct connected in it.