To purchase a UPS to connect to a computer, install the drivers, view the program from this UPS the real consumption of a computer
To consider the capacity of BP - it is necessary for the component to calculate potreblyaya power a graphics card as the CPU/memory as much hard drive as dvd drives so much, as the sound card, usb stick, mobile phone battery, mouse/keyboard so much.
to sum up, give 20-30 percent reserve and to take the appropriate power supply.
Well and, accordingly, capacity has been calculated without printers, speakers and monitor, of course.
for smart UPS, you can still put a real measuring devices between the wall outlet and the PC and measure up, because the BIOSes that upsy, everything else tends to lie in different levels of error