Question Voltage Fluctuation


Apr 20, 2015
Hello, I've noticed that during load, Voltages at +5V and +12V fluctuate, even dropping below the target. PSU is Corsair RM750x (2018), about 2 months old. Notice that i use Phanteks cable extentions. Is there anything wrong with the PSU and should i RMA it, or is this normal? The main reason i'm worried, is that i replaced a 10year old Silverpower 650w for this, but the old one NEVER had a voltage drop below it's "label", and fluctuations were waaaay smaller
CPU: i7 8700k@4.8Ghz, M/b: Asrock Z370 Killer SLI, GPU: 1080ti
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Software readings of voltages are not really accurate and reliable.

The cable extensions are not really very long but depending on the wire gauge and resistance of the wires used I guess they might cause some minute voltage drop.(unlikely)

The RMx 750 are pretty tight in voltage regulation and I'm not sure that much drop (IF it is really happening) is normal for them. Unless if they're really happening and you're unlucky and that unit is faulty.

It's best to ask the guru @jonnyguru to kindly shed some light on this when he can.


Software can't be used to accurately monitor power supply behavior unless it gets that data directly from the PSU (like if you had an RM750i instead of an RM750x as the RM750i actually has reporting functionality).

That said, you can get SOME indications of poor practices from software like that.

1. Extensions. Extensions cause resistance. Resistance causes voltage drops. The higher the load, the higher the resistance, the more the voltage will drop. Why are you even using extensions? Are you using a 1000D case and need 3 foot long cables? Also (Pro-tip): It's not the wire that causes the most resistance. It's the pins.

2. Double check ALL your connections. Particularly the 24-pin. If you're "seeing" the voltage drops in software, it could just be whatever pins that is feeding the motherboard the voltages that the board is reading is not making good contact.

3. Most newer PSUs use sense wire. These are the "double wires" (or two wires in one pin) you see on the 24-pin connector. Essentially, one wire delivers the power and the other wire feeds back to the PSU what the voltage is. If the voltage drops, the PSU can compensate. While these sense wires aren't critical, when you use extensions you essentially eliminate the functionality of the sense wire. The sense wire isn't going to sense voltages beyond the first connection point (where the Corsair cable meets the extension cable), so the PSU cannot compensate for any drops in voltage.