If you’ve gone shopping for a power supply any time over the last few years, you’ve probably noticed the explosive proliferation of various 80 Plus ratings. As initially conceived, an 80 Plus certification was a way for PSU manufacturers to validate that their power supply units were at least 80% efficient at 25%, 50%, 75%, and 100% of full load.
The 80 Plus program has expanded significantly since the first specification was adopted. Valid levels now include Bronze, Silver, Gold, Platinum, and a currently unused Titanium specification level. The chart below lists the requirements a PSU must meet to be certified.
In the pre-80 Plus days, PSU prices normally clustered around a given wattage output. The advent of the various 80 Plus levels has created a second variable that can have a significant impact on unit price. This leads us to three important questions: How much power can you save by moving to a higher-efficiency supply, what’s the premium of doing so, and how long does it take to make back your initial investment?
Power supply pricing and premiums
First, here’s an overview of 80 Plus PSU pricing at various wattages. We created this data from NewEgg results, but only picked units from well-known vendors. Generic products from companies like CoolMax aren’t a part of these results. When we priced units, we opted for the lowest-cost unit from the same manufacturer.
Basic 400W-600W units are quite cheap these days, even from top vendors like Antec, Corsair, OCZ, and Silverstone. Prices start to climb by the 700W range; 1200W units are several hundred dollars.
The price premium for greater-than-80 Plus certification can be substantial. Below 800W, Bronze certification adds 4-20% to the list price of an 80 Plus unit. 80 Plus Gold PSUs are 35-61% more expensive within the same wattage category. Platinum-level power supplies are 90-100% more expensive; twice the price of a standard 80 Plus unit.
By way of example: Antec and Rosewill have $50-$60 80 Plus PSUs in the 501-600W category, while the 80 Plus Platinum products are $139 and $110 respectively. In the 701-800W division, Corsair has 80 Plus Bronze units for $84.95, and 80 Plus Platinum priced at $179.
At the highest end of the market, this changes slightly. Power supplies in the 1kW and greater category don’t put much of a premium on high-efficiency units. An 80 Plus 1200W PSU is $229; 80 Plus Gold is ~$258. 80 Plus Platinum is still significantly more expensive at ~$332.
You can’t save power that you aren’t using
Power supply efficiency is defined as the amount of power actually provided to the internal components, divided by the amount of power drawn at the wall. A 50% efficient PSU that’s tasked with providing 50W of power to a system will draw 100W from the grid. The extra 50W is lost as heat. A 90% efficient PSU would draw 56W in the same circumstances.
Even generic PSUs are far more than 50% efficient; in fact, 75-77% is fairly common. This means the amount of money you save from upgrading to a high-efficiency PSU is minimal if you don’t actually draw much power to start with. Electricity rates are charged by the kWh — if your system only uses 80W at idle, and idles 20 hours a day, you won’t see much benefit from an 80 Plus Platinum PSU as opposed to a regular 80 Plus.
How we tested
We’ve tested two pairs of PSUs from the same manufacturer and with the same rated power output (or close as we could get). Our first testbed was outfitted with two 750W power supplies from PC Power & Cooling. The first is a red Silencer with an 80 Plus certification. Overall listed efficiency for the unit is 83%. The manual breaks this down further, specifying that efficiency ranges from 82-85% depending on exact load.
The other 750W is a Silencer Mark II. It’s certified as 80 Plus Silver with an average efficiency of 85%. Efficiency isn’t broken down by overall load for this model.
The second testbed was configured with a brace of Thermaltake Toughpowers. The first is a 1200W Toughpower 1200A, the second is a 1275W Toughpower XT Platinum. The first unit is certified as 80 Plus, with a listed efficiency of up to 87%; the second’s efficiency is listed as up to 94%. Thermaltake doesn’t provide any additional clarity for either unit, so it’s not initially clear if those figures are for 115V or 220V operation.
Note: The 750W and 1200W figures cannot be cross-compared. We built two entirely different testbeds for this project. Putting a moderate load on a 750W PSU isn’t particularly difficult, while stretching the legs of a 1200W PSU took a bit more work.
Our test methodology was simple: We plugged in a Kill-A-Watt wall meter and measured the power consumption of each unit over 2.5 hours at both load and idle. The meter was reset in between each test for each PSU. Our wattage figures are the average load while the system was in each state, not spot checks on the meter. It’s true that this is a relatively simple, broad-spectrum test, but our goal is to compare simple, real-world savings; not metrics you can’t measure without expensive equipment.
First, here are the idle figures for the four solutions:
The idle figures illustrate what we said earlier regarding the limited impact of increased idle efficiency as far as total power costs are concerned. Gains here are in line with claimed figures. Moving to the 80 Plus Silver 750W cuts idle consumption by roughly 3.6%; the 80 Plus Platinum reduces power consumption by 9.2%.
Load tests show the same gaps at higher power consumption. The 80 Plus Silver 750W Silencer Mark II is 4.5% more efficient than the original Silencer; the 1200W Toughpower XT Platinum is 8.8% more efficient than the 1200A power supply. Again, it matters where you start from. Saving 25W between the 80 Plus and 80 Plus Silver isn’t bad, but the XT Platinum knocks almost three times as much wattage off the 1200A’s main draw.
Clearly the efficiency of a top-end PSU can save you some scratch over the long term. Exactly how much depends on what you’re doing.
How much can you save?
Here, we’ve taken our data from all four power supplies and plugged it into various use equations over an entire year. Our first two graphs assume that the system is either in idle or under full load 24/7/365. Two different costs per kilowatt-hour are included: The US average, at 12.5 cents per kWh, and the current New York State average of 18.7 cents. These are simplistic assumptions, but they ballpark the maximum and minimum savings you’ll see if you never turn the system off.
At constant idle, the 750W 80 Plus Silver saves $4.38 to $6.56 over the course of a year. Upgrading to the 80 Plus Platinum drops between $18.63 and $27.87 back in your pocket.
At constant load, even the modest upgrade offered by the 750W 80 Plus Silver is worth $27-$40. The Toughpower XT 1275W saves you $80-$120 in power costs per year.
Granted, very few people are going to need a power supply under this type of continuous load, but there is a financial benefit to upgrading if you use this much power. At some point, however, we need to address the fact that the best way to save power is to turn the machine off or put it into hibernation.
Here are power usage figures and costs if we assume that the system is idle eight hours a day, under load for four hours, and off/hibernating for the remaining 12.
Heavy workers may still see an advantage from an upgrade; the Thermaltake 1275 XT Platinum will save from $19.57 to $29.38 a year. The smaller 750W upgrade is worth $6 to $9.
A dubious investment
The good news is that power supplies with better 80 Plus ratings really do deliver what they claim — there is a net reduction in total power consumption. If you burn a lot of power, Platinum units could be good investments and pay back their premiums in a year or two. Similarly, if you’re trying to minimize every last watt of consumption, this is one way to do it. The cost premiums, however, don’t add up anywhere but at the highest end. If you’re buying a 1200W unit, Gold is scarcely more expensive and Platinum will still pay back its initial up-front cost in a year or two.
Most of us, however, would be best served by turning the machine off or dropping into hibernation. The best way to save power is simply not to use it, and manufacturers currently charge huge premiums for marginal performance gains. If you’re upgrading from a cheap piece of junk (anything with words like Sparkle, Max, Tech, Sun, Bright, or Beam in the name is virtually guaranteed to be garbage), the premium is easier to justify. If you’ve already got an 80 Plus PSU, it’s a much harder sell.
The flip side is that PSU units go on sale fairly frequently, and a gold or silver unit can be trusted to provide an upgrade. It may not make much sense to buy a unit at a significant premium, but if you get a good deal, we recommend taking it.