Many offices and factories have an Uninterruptible Power Supply (UPS) to feed "critical" equipment the business would not want to "die" in the case of a power dip. A modern UPS works by taking the mains voltage, rectifying it and charging a battery with an appropriate DC voltage. The consumption of the energy stored in the battery during a power dip is what keeps the "critical equipment" running. Trouble is no UPS is 100% efficient. It will generate some heat and usually some noise. If a UPS runs at 66% efficiency (a frightening but realistic figure) 1.52 units of energy (1.52 kWh) are consumed from the mains for every 1 unit of energy (1 kWh) fed to the “critical equipment” on UPS. So for example, your 312 Watt LCD monitor won’t consume 0.312kWh per hour running from the main switchboard, it will in effect consume 0.474kWh per hour running.  If the UPS is in an air conditioned room, the heat the UPS generates will add to the air conditioning load, further increasing the load on your electrical system. If your UPS batteries aren’t in an air conditioned room, you may be voiding any warranty you have on them. So, does all of your stuff on UPS have to be? If the PC has to be, does the monitor?