Or when the AC unit turns on, or when I vacuum the office?

A trend in high end desktops and laptops that is likely to quickly be adopted at all price points is the use of Active Power Correction Factor  (Active PFC) based power supplies.  Active APC has benefits, but mostly for enterprise level use, as it reduces stress on the AC wiring by lowering the current drawn by power supplies with a high Power Factor, which can reach 90% in an Active PFC supply, vs. the 65% seen in typical Passive supplies.  UPS costs are also reduced, as an Active PFC requires less current capacity than the older Passive supplies.  Active PFC supplies don’t use less power, but they do deliver a higher percentage of it when called upon to the PC components.

So what’s the downside and why wouldn’t you want all of your new hardware to utilize Active PFC?  There are two compelling reasons:

• Your existing UPS probably won’t keep an Active PFC based PC running when the power goes off, or during a brownout when the UPS takes over.  This is due to the need for most Active PFC power supplies to be fed a true sine waveform. The majority of the household UPS’s are stepped “simulated” sine, which isn’t a viable source of power for Active PFC based designs.  Data Centers typically use UPS’s utilizing true sine waveform, so see the benefits, but at price points starting at around $500, aren’t a viable option for most home and SMB based computing.
• Active PFC won’t likely reduce your electric bill.  Power Factor isn’t a criterion on which homes and small businesses are billed for electricity. This is true except in the case of commercial utility users who pay for V(oltage) x A(mperes).

Some vendors are providing options for Active or Passive Supplies.  Unless your existing UPS is a true sine wave capable device, or you plan on replacing the OEM supply, strong consideration should be given to avoiding Active PFC.