Put together a new machine today, and ran a quick power consumption test to see what to expect from the total draw.
System specs: i5-6500, Asrock H170M-ITX/ac, 2x4GB DDR4, 1x240GB SSD, Corsair CX-430, Coolermaster Elite 110. Power measurements were made from the wall (240V AC) with a PowerMate Lite.
|Machine State||Consumption (W)||VA||PFC|
(Large FFTs, 4 threads)
In Prime95 the power fluctuated a little, the above entry is a typical value. Peak recorded draw was 73.5W. Maximum temperature hit was 58°C. HwMon recorded individual cores at 3.6GHz, but under Prime95 load they all stuck around 3.3GHz.
You could happily run this machine on a 90-100W power supply. The smallest commonly available PSUs retail tend to bottom out at 350W, which is massive overkill in a system without a dedicated GPU.
(Also, the PFC of the CX-430 — ouch!)