Power supply question!

Running my computer at max stable OC consumes a total of 221W on the Killawatt. I read 215W equates to 180W at the wall so I guess I am using 185W at load.

I use a 180W PSU. How much could it safely output before becoming unstable. I know this would vary depending on the unit but looking for general ballpark figure. Reason I ask is that I will be adding a more powerful GPU soon that will need more wattage so trying to work out my power headroom

 

Well you would need to know the efficiency of the PSU.

So 220W at wall x 80% efficiency = 176W

If you run at peak rated power for that PSU for any length of time or even short times repeatedly, you will burn it out. Efficiency changes too based on temperature and power drawn, so it's a moving target, but should be able to use the published efficiency rating for a close estimation. The more power the system draws from the PSU, the efficiency slowly drops, drawing more power from the wall giving out less to the system. So for even energy consumed, you should be drawing less at the outlet with a larger PSU, although probably not more than a few Watts.

Based on what you're saying, in any case, are running near peak output for that PSU.

Generally, at least from a desktop perspective, you usually want your system running no more than 80% of rated power at peak. So 400W on a 500W PSU.

Also, on the killawatt, are you reading RMS or VA Watt reading? You should be looking at RMS.

 

Not entirely sure whether it is RMS or VA. What is the difference? How do I tell? There are several settings I can choose.

220W is maximum power draw. This with the cpu at max stable frequency and voltage needed to run stable at around 3.5ghz (1.2V) and the GPU also running 1.2V at 790/985mhz (stock 675/800). Simultaneous prime 95 small ffts and furmark!

I need less than 1.15V to run stable at 3.16ghz so could probably cut power by 30 watts. Guess this means should avoid OCing the cpu too much with a more powerful GPU?