Power Supply Using Low Wattage (i Think...)

I recently attached a Kill-A-Watt style wattage meter which plugs into the wall, then my tower plugs into the meter. With my computer running, and the video card going full steam (Video game running to wind up the card), it's only showing a draw of about 166W. My specs are as follows:

Intel i7-3770 3.4GHz Processor
AMD Radeon 7850 Video Card
16 GB DDR3 RAM
2 Monitors on the Radeon, and a third on a USB to VGA adapter
1 SSD Drive
2 SATA spindle drives
2 Fans (One on the case and another on the CPU)
Some misc devices such as a USB 2.0 hub and some speakers etc...

In using a few different online power consumption calculators, the setup should be using around 375W. I understand the with PS efficiency the number I'm seeing on the meter will be slightly different than on the inside end, but the inside value should be lower, as it's probably getting around 80% efficiency, which even further throws the value out. This machine originally had a 275W supply, which started crashing when I updated the video card to the current one, and I installed an 850W supply (currently installed) which resolved the issue. I assumed it was overdrawing on the smaller supply, which is in line with the values derived from the online calculator. Now I'm not sure. Also, I tested the Watt Meter by plugging a toaster rated at 1500W into it, and it read 1498W. Pretty close right? So I'm pretty sure the meter is accurate. Any thoughts on why the draw is so low? Thanks.

 

I don't recall the exact gaming output when I had an HD7850 in my ITX Xeon E3-1230 V2 on a 360W Gold but it was easily sub-200W, probably very close to your logged output . The max draw given by the calculators is for the majority of devices running close to their maximum, something that would be close to impossible with any benchmark utility I've used. Also any 'board chip disabled in the BIOS would result in a slight reduction of consumption.

You can gain details of individual item consumption from running HWiNFO64 with Sensors only, take your heaviest game for a spin and then check the max. outputs/usage % logged. Any overclocking might not be as accurately estimated but I know the eXtreme Power Supply Calculator dev. is actively working on smoothing out most anomalies there.

My approximation of your rig at Outervision (eXtreme PSU calc): http://outervision.com/b/NAE8Ex - it's almost the same result as mine.

My rig @ 3.4/3.8 with a slight voltage boost and my current GTX 970 on a 450W Bronze: http://www.userbenchmark.com/UserRun/798965 - I only briefly see 250+W during benching, whilst gaming it's more likely to be ~220W, if my 360W Gold PSU had a 6/8-pin PEG instead of just a 6-pin, I'd be comfortable using that.

 

I know it's sort of a generic question, but any ideas why it would shut down with the 275W supply, and run fine with the 850W?

 

Could be a bad connection anywhere, PSU/motherboard problem, things like that are hard enough to pinpoint even if you do have another good rig to test with. A 275W PSU when new might just have held up - if it was of a modern design and well built. If it was an old design or a poor build, chances are that it would never run your hardware under full load.

Also, many watt meters might only poll the line at maybe 1 per second or so, they'll never catch the micro/transient peaks that might draw +30-50% for a few milliseconds.

A couple of PSU reviews, one of a cheap, bad 500W, another of a quality 550W, tested just a few days apart:
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=324
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=323