Which PSU should I buy?

fadedorca66 said:I just find that whole expression 😁
totally hilarious.

Honestly, I've heard it so often it doesn't even register anymore.

I'm building a monster rig here—and by that, I mean I'd much rather have one beefy unit than two weak ones—but the connector count is killing me. So far, the only thing looking decent is the Corsair RM1200x with its 10 x pcie 6+2 pins.

How much can I actually lean on the EPS vs the PCIE? From what I can tell, the "standard" 6+2 pin has three 12V pins and five 0V pins. Unless there’s some catch I'm missing?

Terry Collins9 said:...How much load can I actually put on the EPS vs. the PCIe connectors? From what I can see, the "standard" 6+2 pin setup only really has three pins carrying 12V, while the other five are just ground. Is there some kind of catch I'm missing here?

Not really, there isn't any catch. Whether it's a 6-pin or an 8-pin, those three specific pins are the ones actually providing the voltage (up to 150W total), while the others serve as ground. Those two extra pins are essentially just for sensing; they exist so the PCIe device can verify it's connected to a sufficient power supply, though I know some cards tend to ignore that check entirely.

So, with an EVGA SuperNOVA 1200 could I actually hook up five GPUs without everything going south?

I just realized the RTX 2080 super I have coming is going to need dual power—which totally messes with my math. Plus, there’s still the power requirements for the PCIe risers (I'm looking at those BTC 37 boards).

Check if those cards with 2x8-pin connectors actually need both to function. Some cards that come with a 1x6-pin can run without that extra one—meaning just off the motherboard—or when you have an 8+6 setup and skip the 6. Besides, you’re going to undervolt anyway; it shouldn't be pulling more than 150W. We're talking about "edge cases" where that last connector isn't strictly necessary. I'm pretty sure my RX580 would run fine with just the 8-pin despite having the 8+6 layout, and I bet some RX460s could pull enough power straight from the PCIe slot even if they were rated for a 1x6-pin

I'll run some tests and see what happens.
I just read today that the GPU pulls up to 75W straight from the slot, with everything else coming from the extra power cables—is that right? Guess I'll have to go out and grab some multimeter clamps, even if I only end up using them once.

wiredotter14 said:You should check if those cards with dual 8-pin connectors actually require both plugs just to function. Some cards that come with a single 6-pin connector can run without that extra bit—meaning they draw enough straight from the motherboard—or even when you have an 8+6 setup and skip the 6-pin. Since you're planning on undervolting the card anyway, it shouldn't be pulling more than 150W. We're really just talking about those "edge cases" where that last connector isn't strictly mandatory. For instance, I'm fairly certain my RX580 would run fine with just the 8-pin despite having an 8+6 layout, and I believe some RX460 models could even run without any PCIe power at all, even though they were rated for a 6-pin.

My own RX 580 only has a single 8-pin, yet it runs perfectly fine on the 6-pin alone without asking for those extra 2 amps. On the other hand, my old Black Titan has an 8+6 setup, and it won't even allow the system to boot unless those two extra pins are connected; if I try running it with just 6+6, it basically refuses to start because it's demanding those last 2 pins. Is this perhaps a quirk mostly found with Nvidia hardware? It seems like AMD is a bit more relaxed and lets things just go their own way.😬 Maybe we'll need to consult some online prophets if anyone wants to debate this further.

From what I can tell, the power supply mentioned here has 8x8 PCIe connectors... so that covers three cards if they are 8+6 setups. For the remaining two, you can just grab two of those PCIe cables from Best Buy that we were discussing recently:

https://www.amazon.com/delock-pcie-cable...erni-202300065

That way, you don't have to mess around with cables for any other components. Just apply an undervolt, and everything should work smoothly.

https://www.amazon.com/Delock-Adapter-Cable-PCI-Express-Connector/dp/B07D8S5YJ8

Hmm, looking at this—it’s a 6-pin to dual 8-pin setup, so I don't think it'll actually solve anything for me. I already ordered the EPS to PCIe adapter from China. Right now, only one GPU requires dual power anyway—so the math says one connector should cover both the card and the slot.
Plus, this PSU would just be a secondary unit—not like I need it to power the motherboard.

Terry Collins9 said:From what I can tell, that cable is just a 6-pin to dual 8-pin setup, so I'm not sure if it would actually solve my problem. I already ordered an EPS to PCIe adapter from a vendor overseas. For now, only one of my cards requires dual power connectors, so my logic is that a single connector should be able to handle both the card itself and the slot power.
Plus, this PSU would really just be a backup, so I don't actually need it to power the motherboard.

But why worry? Like we discussed, those extra two pins are just for sensing... trust me, it works; I’ve seen an 8+6 card running off a single 6-pin connector before without any issues. The real question isn't about the connection, but whether the power supply can actually provide enough juice to keep everything stable.

Yeah, depends on the card. Honestly, I don't get why my RX580 even has an 8+6 pin setup, though I guess it might be useful sometimes since it probably pulls less—or basically nothing—directly from the motherboard. I have no idea what happens when you're running six cards and each one is pulling 50-75W through the board...
And I'm not sure if skipping one of those 6-pin connectors actually increases the load on the slot itself, or if the power draw is just hard-coded regardless.

wanderingbison9 said:Why? We already established those extra +2 pins are just for sensing... trust me, it works. I’ve seen an 8+6 GPU setup running off a single 6-pin connector before. The real question isn't about the connection—it's whether the PSU can actually handle the juice.

Hold on, aren't those +2 pins actually part of a voltage rail? 😁
You live and learn... 🤔

wiredotter14 said:Yeah, it really just depends on the specific card. Honestly, I’ve never quite understood why my RX580 comes with an 8+6 pin setup, though I suppose it could be a benefit in certain scenarios since it likely draws less—or maybe nothing at all—directly from the motherboard. I can't help but wonder how things stack up when you have six different cards running, where each one might be pulling anywhere from 50 to 75W straight from the board....
And I’m not entirely sure if leaving a 6-pin connector unplugged actually increases the load on the PCIe slot, or if there's a set limit on how much power it can draw regardless.

It's most likely because those cards are designed to be pushed quite a bit past their stock settings, provided you have decent cooling...😉 Those extra 6 pins are there to provide that extra headroom for maintaining clock speeds when needed, even if they aren't being fully utilized all the time. And let's not forget that Nvidia has its own automated overclocking feature running in the background on almost all their cards, so they probably insist on having the full 8+6 connected just so they can pull more juice for that hidden boost.

wiredotter14 said:Wait, aren't two of those pins in the +2 meant for voltage? 😁
You live and learn... 🤔

No, those are just sense and ground pins; the actual voltage lines are only the 6 pins, consisting of 3 voltage lines and 3 ground wires.

wanderingbison9 said:Look, we already covered this—those extra +2 pins are just for sensing... trust me, it works. I’ve seen an 8+6 GPU setup running off a single 6-pin connector before. The real question isn't the connection, it's whether the PSU can actually handle the juice.

I think you missed my point entirely. I'm asking about plugging a 6+2 into an 8-pin CPU header.

wiredotter14 said:Wait, aren't those extra +2 pins part of the voltage rail? 😁
You live and learn... 🤔

Here's a picture—try to keep up.
It seems weird to me too.

Are you saying for GPUs that require those +2 pins, you just plug in the +2 alone?

Terry Collins9 said:I don't think you quite caught my drift. What I'm trying to do is plug a 6+2 connector into an 8-pin CPU slot.

Yeah, I follow you now, but I'm just wondering why on earth you'd try that if your power supply already has 8x6/8-pin PCIe connectors available? Are you actually planning on trying to power the CPU using a PCIe cable???

wiredotter14 said:I'm not really sure what happens when you hook up 6 cards where each one is pulling 50-75W directly from the motherboard...

I guess if you use a riser, that 50-75W the GPU would normally grab from the board actually comes through the riser instead (which is why you plug the riser into a Molex or SATA connector from the power supply).

fadedorca66 said:I'd say once you plug in a riser, that 50-75W the GPU would normally pull from the motherboard actually comes from the riser instead (which is exactly why those things connect directly to a Molex or SATA connector from the PSU).

Yeah, right. As if.

wanderingbison9 said:Probably because they designed it to be pushed way past stock settings, provided you have decent cooling.😉 The +6 pin is just there to pull extra juice if it needs to maintain the clock speed; it doesn't mean they're constantly drawing full power. And let's not forget that Nvidia has that proprietary automatic OC running in the background on all their cards. That’s exactly why they insist on having both the 8-pin and the 6-pin connected—so they can siphon more power for that hidden OC.
No, common sense and grounding—it’s just those six wires: three hot, three neutral, plus the ground.

The RX580 pulls about 150W (theoretically). My PowerColor Red Dragon uses an OC BIOS that pushes that TDP up to around 180W. Between the 8-pin and the PCIe slot, you're looking at 225W total. If you add a 6-pin, that hits 300W. Personally? I don't see much point in using the extra 6-pin, but hey, if it lets the card suck less juice from the motherboard and raises the ceiling, fine. Whatever.

I'm running them at a +50% power limit, so sometimes they'll pull over 200W.

wanderingbison9 said:Yeah, I get where you're coming from—but why would anyone try to power a CPU using a PCIe cable? Makes zero sense, right?

Because I’m trying to run five different GPUs—which is a nightmare since most power supplies only give you four VGA connectors. Even those massive 1500W units.
I need enough juice for the slots too.

Terry Collins9 said:Because I'm trying to power five different GPUs, which is tricky since most power supplies usually max out at four VGA connectors—even those massive 1500W units.
I also need to make sure I can handle the power draw from the slots themselves.

My mistake, though—I misread the number of PCIe connectors listed. It says eight, but looking closer, it’s actually 4x6 + 4x2... I suppose those extra 2-pin ones don't really function on their own without being paired with a 6-pin, so now I see why they're counted separately...

wanderingbison9 said:Alright, fine—I misread the number of PCIe connectors. They listed 8, but it’s actually 4x6 + 4x2... I guess those extra 2 don't really do anything on their own without being paired with a 6, so now I get why they count them separately...

Yeah, I thought the same thing until I finally cleared the cobwebs out of my eyes and took a closer look.

It turns out I’ve been calculating the power requirements all wrong (apparently). On top of the TDP, I figured I should add another 75W just to cover the slot/riser power. But the GPU pulls its total draw from both the slot and the cables combined. Which means—wait for it—I don't actually need such a massive power supply. What really matters is the sum of the TDP plus the motherboard, CPU, and everything else.

People always suggest adding a 20% buffer to your power calculations, but honestly? I have no idea why—maybe it's just wishful thinking—and it doesn't make much sense to me. The actual wattage the card pulls is basically the TDP (sure, it might spike during an overclocked gaming session, but I won't be doing that) and it usually sits around 70% capacity. Even if things go sideways and settings reset to default, the card isn't going to suddenly start pulling max power again. An RX 570 8gb pulls about 135W (150W TDP), and an RTX 2060 pulls 130W (160W TDP)—that's only about 80-90% of the rating.

When you're modding a BIOS, you really ought to be able to set the TDP right there—and it shouldn't just reset itself on its own. If you underclock or undervolt the card below that threshold, it shouldn't throttle. Personally, I don't think an RX580 with a 110W TDP would have any throttling issues while mining.

Terry Collins9 said:I honestly thought the same thing until I finally cleared my vision and took a closer look at the numbers.

It turns out I’ve been calculating the required power slightly incorrectly all this time, or at least that’s how it feels. Beyond just looking at the TDP, I figured I should probably tack on an extra 75W just to account for powering the slot or the riser. But when you think about it, the GPU draws its total power through both the slot and the cables combined. This realization suggests that I don't actually need such a massive power supply after all. Ultimately, what matters to me is the sum of the TDP plus the power draw from the motherboard, the CPU, and everything else in the loop.

People often suggest adding a 20% buffer to your total wattage calculation, but I can't quite wrap my head around why that's necessary—maybe it's just wishful thinking on my part—because it doesn't seem to make much sense to me. The actual power the card pulls is usually right around its TDP (though it might spike higher during overclocking for gaming, which isn't something I plan to do), and for most tasks, it'll likely hover around 70% capacity. Even if things go sideways and settings reset back to defaults, the card won't suddenly start pulling its maximum rated power. For instance, an RX 570 8gb pulls about 135W despite having a TDP of 150W, and an RTX 2060 pulls 130W with a TDP of 160W, which means they are typically operating at roughly 80-90% of their limit.

Just be careful if you're planning to pull that 75W for the slot or riser using SATA or Molex cables, because those aren't really designed to handle 75W; they're generally rated for about 54W, though you might get away with it if multiple connections are spread out. On the other hand, a PCIe connection with a 6+2 pin connector is rated for 4.16A per rail, which works out to about 150W, while SATA and Molex are limited to 1.5A per rail, totaling around 54W. That said, the PCIe slot itself is technically capable of handling up to 288W if you're drawing 8A per rail.