Looking at various power supplies I see some of them listed as 80PLUS with various metal combinations. What does the 80PLUS label represent and how more efficient are they compared to ones without the label?
80 PLUS simply means that the power supply is 80% or more efficient at various levels of power output relative to its rated maximum. The "metal combinations" signify varying conformance to this target at different fractions of maximum rated power output. Here is a table with the various levels:
Greater than 80% efficiency means that less than 20% of the power input becomes something other than the desired DC voltage (for example heat). Efficiency, simply enough, is the ratio of input power to output useful power (or more generally, useful work performed by a device).
In terms of raw numbers, this means that a power supply rated for 500W output will, under full load, require a maximum of 125W that does not contribute to its useful DC output. According to AN46 - Efficiency and Power Characteristics of Switching Regulator Circuits, switching power supplies (of which PC power supplies of today are a subset) typically range from 70% to 90% efficiency, so >80% gives you a ten percentage point boost over an "inefficient" supply converting 70% of the input power into useful DC. At 500W output, that translates to approximately 90W power saved going from 70% to 80%, although the exact numbers are likely to vary between various PSUs, rated maximum loads and actual load at the time of the measurement (switch-mode power supplies have a base load for their internal circuitry, which remains largely or entirely constant regardless of the output power drawn).
80Plus is an energy efficiency certification program. There are different levels of certification depending on how effecient the PSU is: standard, followed by bronze through to platinum (there's also a Titanium grouping for 230V intervals). The ratings are based on how much power is being lost at different loads. The difference between bronze and platinum tends to be around 10% efficiency, with the bronze PSUs running at around 80% typically.
Check out the full list of power supply manufacturers and their certified products here.
It is supposed to be a standard for PSU efficiency. There are several sub-levels - for more info see here
Generally I would expect an 80PLUS PSU to be more efficient than an "unlabelled" one.
Like Prang said, it's an efficiency standard developed to make sure PSUs don't waste power.
See below from Wikipedia:
80 Plus (trademarked 80 PLUS) is a voluntary certification program intended to promote efficient energy use in computer power supply units (PSUs). Launched in 2004 by Ecos Consulting, it certifies products that have more than 80% energy efficiency at 20%, 50% and 100% of rated load, and a power factor of 0.9 or greater at 100% load. That is, such PSUs will waste 20% or less electric energy as heat at the specified load levels, thus reducing electricity use and bills compared to less efficient PSUs. Sometimes, rebates are given for manufacturers who use 80 Plus-certified PSUs.