Yes, the PSU itself consumes less than a watt. I assume that MB consumes about 3 watts and that's 3 - 4 watts in sum. That's what my power meter shows. It's completely OK. But 4 W at 230 V is just 4/230 = 0.017 A. That's active current. And my power meter shows about 0.17 A, so the remaining current is 0.17 - 0.017 = 0.153 A and that's reactive current. I assume that it goes through the X-caps that are part of the input PSU filter. So I wonder which capacity they have.That’s not your power supply—it’s other system components, including any LEDs remaining on. The power supply consumes a fraction of 1 Watt when in standby mode:
But now I've noticed the following line in the table at the page you linked: Test #3, 5VSB@0.55A = 3.588W input power with 0.091 PF. 3.6 W is very close to my case. But since power factor is 0.091, the current that PSU consumes is much more, it's (3.6/0.091)/230 = 0.172 A! And that's very close to my measurements.
Probably that's the reason why this PSU is marked as "Vampire power".