Idle Power Supply Energy Consumption

No it wont. More likely it draws around 10 watts give or take at a light load.

However that said the whole 250 watt power supply to drive single 3.5 SATA drive sounds like gross overkill to me.

All of my 3.5" SATA drives I use as external storage devices run off of the 5 volt 1 amp USB port source without issue.

Unless you are running some 50 drives simultaneously yes its wasting power even if its only has a 10 watt standby power draw.

I have a USB to sata interface with extra 5v power and the hard drive will not work with this because it also needs 3v, 5v and 12v on different pins. The hard drive does spin up as I removed the drive from my computer to test it. How do you power yours on 5v? Also, my reason for buying a proper power supply is that I have read many reviews of the cheap ones in kits exploding and destroying hard drives.

Buy a proper power supply. Then, unplug it when you are not using it.

It has a built in converter power supply. I just plug it in and way it goes. I got it on eBay for around $15 a few years ago.

Although now that I think about it it may actually draw 1.5 or 2 amps not one. What ever the maximum power a USB port puts out is what it runs on. The thing is most of the newer hard drives take far less power to run than the older models did despite having far greater storage capacity.

Still I have an older USB adapter for ATA type hard drives and that is powered by a 1.5 amp 12 volt power pack but still the power pack is only about 20 - 25 watts input at most if I am remembering correctly.

My Gateway laptop is using 41 watts @.6 amps right now, as I type. The battery That's at 118.4 Hz.

Power factor .55.

It is charging, slightly, because I unplugged it for 5 minutes.

Almost no current is draw by an idle power supply. I tested 3.

I did get a reading of .01 amp when I plugged an idle shaver power supply/charger in. No volts registered.