Guide

How to read a PSU label, including 12V-2x6

The big number on the box is the continuous rating. A label that says 850 W means the supply is designed to deliver 850 W without stopping, at the temperature and input voltage the maker states. It does not mean the supply can deliver 850 W on the 5 V rail, and it does not mean a 1 millisecond spike of 1700 W is outside the design if the unit is ATX 3.1 and has a 12V-2x6 connector.

Start with the 12 V rail

A graphics card and the CPU EPS connector live on 12 V. Older labels split 12 V into rail 1 and rail 2. Add those 12 V currents and multiply by 12 if you want watts, and compare that to the card. A modern single-rail label prints one 12 V current, often close to the total wattage divided by 12. If the 12 V figure is far below the headline wattage, the headline is being filled by rails the PC barely uses.

The side sticker also lists 5 V and 3.3 V combined, and often a note that the combined 3.3 V plus 5 V power is capped. That cap matters for old drives and some fan hubs. It is not the GPU budget.

80 PLUS is a floor at three load points

The badge is a certification, not a curve of the unit in your hand. On 115 V internal desktop supplies, CLEAResult publishes floors at 20%, 50%, and 100% of rated load. Titanium adds 10%. Gold, for example, is 87% / 90% / 87% at those three points. The best published point is 50%, which is why WattWise's efficiency size aims there. A unit can beat the floor. The badge does not prove that it does. The payback calculator uses the floors and asks you for the price gap.

12V-2x6 and the sense pins

The 12V-2x6 connector replaced 12VHPWR. Four sense pins tell the card which cable is attached. Intel's ATX design guide, document 336521, Table 3-6, following PCIe CEM 5.1, maps them like this:

• Both sense pins grounded: up to 600 W sustained after configuration.
• One open and one grounded: 450 W.
• The opposite pair: 300 W.
• The two pins shorted to each other, floating from ground: 150 W.
• Both open: the card should not draw on that cable.

The card may draw that cable budget in addition to the slot, which is up to 75 W. A native cable from an ATX 3.1 supply sets those pins inside the supply. An adapter dongle sets them for the rating printed on the adapter. Seat the plug until the latch clicks. A half-inserted high-current connector is a heat problem the wattage number will not fix.

The same document's Table 3-3 says a supply above 450 W with that connector must hold 200% of its label for 100 microseconds, 180% for 1 ms, 160% for 10 ms, and 120% for 100 ms, at the duty cycles in the table. Continuous power stays at 100%. That is why WattWise does not double the shopping number for a spike. The transient guide walks the two columns, including the lower one for supplies that omit the connector.

What to ignore on the box

"Peak" and "max" in marketing type, printed larger than the continuous number, are not the continuous rating. Cybenetics and 80 PLUS are different programs. A Gold badge does not tell you the hold-up time, the fan curve, or whether the 12V-2x6 cable is included. Read the sticker for watts and amps, the badge for the efficiency floor, and the cable for the sense-pin rating. Then use the calculator for the continuous load of the parts you actually chose.

Sources: Intel document 336521 and CLEAResult's 115 V internal table.