Corsair CX750 vs. Corsair RM750 vs. Corsair RM850?

Kadence

Senior member
Nov 18, 2004
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I had a Corsair 1000HX power supply that recently died.

For a replacement, I don't think I need the fully 1000W - 750+ watts should probably do. However, I do need one with the same power connectors, so I'm thinking of going with Corsair again as I'm assuming the connectors would be the same (please correct me if I am mistaken).

Right now I'm trying to decide between the CX750 ($90), RM 750 ($130) and RM 850 ($145).

The CX750 is "Bronze" certified, the other two are "Gold" certified. Does anyone know what the difference between Bronze and Gold is?

Also, is the RM 850 a significantly better unit than the RM 750? Other than the wattage, are they essentially the same?
 

lehtv

Elite Member
Dec 8, 2010
11,900
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Those seem to be newegg prices so I'm assuming you're in the U.S. Those CX and RM units are overpriced. You can get better quality units for less in each efficiency and capacity class.

You don't need as many connectors as in 1000HX which had six PCIe connectors. if I'm not mistaken, your graphics cards use three PCIe connectors in total. Even many 650W units have four PCIe connectors.

I would buy one of these at the moment:

XFX 750W XXX Gold $105 ($85 AR) @ NCIX
It's a copy of Seasonic X750 which is better than Corsair RM750. See reviews by JonnyGuru: Seasonic X750, Corsair RM650, Corsair RM850. Also, review by the XFX 750W XXX itself by hardwaresecrets.

Rosewill Capstone 750W $100 @ Amazon
A fine choice as well, it's an all-round high performance unit that also uses better capacitors than RM series. 7 year warranty.

I'm thinking of going with Corsair again as I'm assuming the connectors would be the same (please correct me if I am mistaken).
The types of connectors used are the same across all units, just the number of each type differs. The number of connectors mostly depends on how powerful the unit is, but there are some differences between brands as well. But buying a Corsair unit doesn't mean it will have the same number of connectors as another Corsair unit, even if they had the same labeled wattage. Usually equally powerful models within the same brand have some minor differences in connectors.

The CX750 is "Bronze" certified, the other two are "Gold" certified. Does anyone know what the difference between Bronze and Gold is?
It refers to efficiency, that is, the percentage of AC intake watts that turn into DC watts for the components. The higher this number, the less waste heat is produced by the PSU. This can increase the lifetime of its internal components. High efficiency also means the PC uses less electricity, which affects your electricity bill. 80+ Bronze efficiency is roughly between 82-87% (depending on the particular unit and the load) in the North American 120V network. 80+ Gold efficiency is about 87-90%.

In a PC consuming as much power as yours, and with an average cost of electricity, you'll save a few dollars per year going with a Gold unit instead of Bronze. If you leave the PC on 24/7 and/or have relatively high cost of electricity, a Gold unit might pay itself back as an investment compared to buying a Bronze unit.

A common misconception is to think of 80+ ratings as some sort of quality ratings. You can think of efficiency as being a part of quality but what really matters for quality is reliability, and efficiency doesn't directly imply reliability. A highly efficient unit can be unreliable and a not so efficient unit can be extremely reliable. It's just coincidental that often highly efficient units are also reliable since high efficiency is costly to manufacture, so customers expect the units to actually perform well too.

Also, is the RM 850 a significantly better unit than the RM 750? Other than the wattage, are they essentially the same?
Wattage is most likely the only difference.
 
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TemjinGold

Diamond Member
Dec 16, 2006
3,050
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Is the Corsair out of warranty? Your cards suggest you are a gamer and given how old they are, I'm guessing money is tight. If so and the Corsair is in warranty, why not RMA it and use the cash to upgrade to a modern single card?
 

Torn Mind

Diamond Member
Nov 25, 2012
8,713
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80+ enforces quality only indirectly, by requiring the test unit to deliver its rated wattage at room temps. Thus, it weeds out many PSUs that are not labelled honestly and unwittingly killed by the user when a part that pulls a lot of current overloads a particular component.
 

lehtv

Elite Member
Dec 8, 2010
11,900
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80+ enforces quality only indirectly, by requiring the test unit to deliver its rated wattage at room temps. Thus, it weeds out many PSUs that are not labelled honestly and unwittingly killed by the user when a part that pulls a lot of current overloads a particular component.
Good point. However, testing in room temperature doesn't weed out the units that fail in temperatures common to a typical ATX tower that also houses components that consume (and thus radiate) as many watts as the unit is rated for. A PC consuming "only" 500W would heat up the internal air far higher than room temperature, even with a good fan setup. If a 500W unit can hold its own at 25°C, it implies absolutely nothing about operation at 40°C.

Also, to my knowledge, 80+ tests the rated wattage for peak wattage, not continuous operating wattage.
 
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Torn Mind

Diamond Member
Nov 25, 2012
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Good point. However, testing in room temperature doesn't weed out the units that fail in temperatures common to a typical ATX tower that also houses components that consume (and thus radiate) as many watts as the unit is rated for. A PC consuming "only" 500W would heat up the internal air far higher than room temperature, even with a good fan setup. If a 500W unit can hold its own at 25°C, it implies absolutely nothing about operation at 40°C.

Also, to my knowledge, 80+ tests the rated wattage for peak wattage, not continuous operating wattage.
Yes, all reasons to not just blindly look at 80+ ratings as if they had considered all these factors that could affect reliability and proper performance when they certainly have not.

In addition, it seems that companies can get the sticker for one unit and then stick those labels on an inferior unit. Some reviewed unit at either Hardware Secrets or jonnyGURU had one such unit, but I can't remember exactly where I saw it...
 

Kadence

Senior member
Nov 18, 2004
275
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Thanks so much for the detailed response lehtv!
Is the Corsair out of warranty? Your cards suggest you are a gamer and given how old they are, I'm guessing money is tight. If so and the Corsair is in warranty, why not RMA it and use the cash to upgrade to a modern single card?
It was actually bought in July 2008, so it's not under warranty. And no, money isn't really a major issue.

And actually I haven't updated my sig, I have an HD7950 graphics card. Thanks :)
 

lehtv

Elite Member
Dec 8, 2010
11,900
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For a single 7950 and a Q9650 both overclocked, 550-650W is optimal. If you intend to go Crossfire, then 750W-850W is the sweet spot. But you'll be upgrading your CPU, motherboard, RAM and adding an SSD first, so I don't really recommend spending any extra on the slim chance of ever buying a second card for Crossfire (or upgrading to dual card setup with some other GPUs).

However, looking at the prices of 650W units comparable to the ones I linked... the XFX 750W is still the cheapest after rebate. I'd go with that.
 

Yuriman

Diamond Member
Jun 25, 2004
5,530
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For a single 7950 and a Q9650 both overclocked, 550-650W is optimal. If you intend to go Crossfire, then 750W-850W is the sweet spot. But you'll be upgrading your CPU, motherboard, RAM and adding an SSD first, so I don't really recommend spending any extra on the slim chance of ever buying a second card for Crossfire (or upgrading to dual card setup with some other GPUs).

However, looking at the prices of 650W units comparable to the ones I linked... the XFX 750W is still the cheapest after rebate. I'd go with that.
This. I have a similar system that's actually running happily on an Antec 430w at stock. 550 would likely suffice when overclocked.
 

KentState

Diamond Member
Oct 19, 2001
8,397
392
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However, looking at the prices of 650W units comparable to the ones I linked... the XFX 750W is still the cheapest after rebate. I'd go with that.
I purchased on these, maybe off your recommendation and it's probably the best 750w PS available IMO. The price is great, Seasonic sourced, modular and all the reviews show that it's very efficient, potentially platinum across the board if submitted for that level of testing.
 

DigDog

Lifer
Jun 3, 2011
12,459
1,448
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damn, seems like everything worth saying has already been said.

oh well, enjoy your new 750w XFX psu.
 
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