It is an Intel "guide" for power supplies, but has been "adopted" by United Laboratoreies and the English EN 60950.
Actually, the 12V 2.01 is the design specification released in June, 2004 which updated the ATX12V power supply specification. The "2.01" means that it is Version 2.01 of the specification, and that the ATX 12V specification has been updated to 2.01 so that it will fully power PCI-Express devices.
Not that it really makes any difference, but to bore you... The newest power supplies, are version 2.03. Newegg and others post the version because it is the easiest way to know what you are getting. Some new boards will require 2.03, but most specifications are intended to provide direction for future requirements.
These are part of the US UL, and English EN 60950 engineering specification standards that are used pretty much world wide...
"System components that use 12V are continuing to increase in power. In cases where expected current requirement is greater than 18A, a second 12 V rail should be made available. ATX12V power supplies should be designed to accommodate these increased
+12 VDC currents."
and
"Minimum measured efficiency is required to be 70% at full and typical (~50%) load and
60% at light (~20%) load. New recommended guidance has been added to
The 2 x 10 main power connector has been replaced by a 2 x 12 connector. This was made to support 75 watt PCI Express requirements. Pinout assignments are based on the SSI recommendation.
With the added 12V, 5V, and 3.3V pins the need for an Aux Power connector is no longer
needed and the guidance for this connector has been removed.
The 12V rail on the 2 x 2 power connector should be a separate current limited output to meet the requirements of UL and EN 60950.
Almost gobbledygook, but important stuff for designers. The guide is updated yearly, anticipating the future, so that all manufacturers are on the same page.
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