PCI-SIG, the organization behind PCI(e) standards, Cautions against using 8-pin to 12VHPWR adapters. It can get hot, which can lead to dangerous situations.
Heavy video cards can supply a lot of power via a 12VHPWR connection. The 16-pin connector can carry up to 55 amps, which is the equivalent of 600 watts at 12 volts. The connection can also absorb high current peaks (200%).
Most ATX 3.0 power supplies will have a 12VHPWR connection, but with older power supplies, you’ll have to deal with an adapter. Cards like the RTX 3090 Ti come standard with a 3x 8-pin to 12VHPWR adapter, but 2x 8-pin to 12VHPWR adapters are also available.
connector requirements of Standard ATX 3.0.
However, these 8-pin connectors can handle a much lower current: a maximum of 13.5 amps (more than 150 watts). With a 2x 8-pin to 12VHPWR converter, it will go through twice that with a heavier load (not counting any current peaks), and you won’t save 600 watts with three 8-pin connections.
Then of course the question is whether this adapter distributes power evenly over the 8-pin cables, and Wccftech has Tested for us. On the RTX 3090 Ti, which was using 450 watts at the time, 282 watts went through the first 8-pin connector; Almost double what is intended. The other two connections are not loaded with more than 80 to 100 watts.
So it looks like you really need an ATX 3.0 power supply for high-end video cards. Fortunately, mid-range RTX 4000 cards seem to be more economical: the RTX 4070 is expected to draw “only” 300 watts, which it provides only with two 8-pin connectors.
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