7870 and 400W PSU

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7870 and 400W PSU

Postposted on Tue Apr 02, 2013 10:43 am

I bought a 7870 just yesterday and it just hit me that I didn't check if my PSU was good enough for it. I know AMD recommends a 500W one but I figure they may overestimate, so can anyone tell me if I'll be good with this set up i.e. not toast my whole rig :o or should I really get a new PSU.

Intel i3 530
Corsair 4GB RAM
HD 7870 (5770 currently which 'needs' 450W)
400W Corsair CMPSU-400CXUK/400CX
Gigabyte H55M-UD2H
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Re: 7870 and 400W PSU

Postposted on Tue Apr 02, 2013 10:51 am

TR used roughly the same system you have for their 7870 review. They measured 205W system power draw under load. You can also plug your system into a power supply calculator to get a recommended PSU wattage. (which recommends 380W for your system) Keep in mind that overclocking pulls extra juice too.
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Re: 7870 and 400W PSU

Postposted on Tue Apr 02, 2013 10:58 am

In addition, there's a simple way to look at it- does your power supply have the appropriate connectors, and if so, does it have the proper 12v amperage? You have a quality modern unit, so the answer is likely yes. Remember that those numbers Nvidia and AMD recommend are based on lowest-common-denominator predictions.
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Re: 7870 and 400W PSU

Postposted on Tue Apr 02, 2013 11:00 am

I have a "similar" set-up.

Core i5 3470
8GB of ram
7870 1Ghz
60GB SSD
240GB SSD

With a 430 watt Corsair CX power suppply.

No problems at all playing Borderlands 2/StarCraft II HotS on max graphic settings. You're fine. Enjoy the system.
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Re: 7870 and 400W PSU

Postposted on Tue Apr 02, 2013 11:15 am

I think I'll go for it :-? I'm sure it will be fine but I was just wondering is there any possibility of it damaging the rest of my rig if it isn't sufficient? Any thing to look out for etc.

Thanks all of you btw
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Re: 7870 and 400W PSU

Postposted on Tue Apr 02, 2013 12:22 pm

If you're unsure and not feeling comfortable, get a 500.

But like DPete27 said, your system runs around 205W under load, so you still have a very high margin of error. Power supply companies love marketing up their kilowatt power supplies because in their minds, bigger numbers = better
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Re: 7870 and 400W PSU

Postposted on Tue Apr 02, 2013 12:39 pm

You'll be just fine. :)
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Re: 7870 and 400W PSU

Postposted on Sat Jun 08, 2013 7:35 pm

Buying an expensive 80+ Gold 750 or 850 Watt PSU might seem like overkill, however in your system you will always be running it in it's peak efficiency range and will save you quite a bit of money over time compared to a PSU which will be running at over 75% all the time.

Also what happens when you upgrade your system in the future (crossfire for instance)? All of a sudden you need a new PSU and the lower price of the 400 Watt PSU is no longer looking so good.
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Re: 7870 and 400W PSU

Postposted on Sun Jun 09, 2013 8:14 am

Throw in the card and give it a shot. I think you will be ok. Your cpu Loaded at 100% uses around 105-110 watts stock @ 4.0 ghz it uses around 145-155 watts.

Since most games put most of the stress on the gpu and the cpu might hit 50%. Metro Last light Has pretty high cpu use....even though it is a single player game I have gotten higher cpu use during gameplay then BF3 multiplayer. Thats with 4+ ghz to 4.8 ghz on my 2600k.

But during normal gaming It's pretty hard to get 100% cpu usage if your using a good CPU these days.
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Re: 7870 and 400W PSU

Postposted on Sun Jun 09, 2013 11:38 am

Nec_V20 wrote:Buying an expensive 80+ Gold 750 or 850 Watt PSU might seem like overkill, however in your system you will always be running it in it's peak efficiency range and will save you quite a bit of money over time compared to a PSU which will be running at over 75% all the time.

Also what happens when you upgrade your system in the future (crossfire for instance)? All of a sudden you need a new PSU and the lower price of the 400 Watt PSU is no longer looking so good.

Peak efficiency range is around 50-80%. I don't see how a system pulling 200-250W is at that range if you put a 850W PSU.
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Re: 7870 and 400W PSU

Postposted on Sun Jun 09, 2013 1:45 pm

You can probably limp along with what you have for now, but PSUs lose output as they age so at some point you'll need a new one--start cruising retail sites for a good deal while time is not a factor. I would recommend something in the 600 watt range as it should put you in the efficiency sweet spot.
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Re: 7870 and 400W PSU

Postposted on Sun Jun 09, 2013 6:02 pm

Flying Fox wrote:
Nec_V20 wrote:Buying an expensive 80+ Gold 750 or 850 Watt PSU might seem like overkill, however in your system you will always be running it in it's peak efficiency range and will save you quite a bit of money over time compared to a PSU which will be running at over 75% all the time.

Also what happens when you upgrade your system in the future (crossfire for instance)? All of a sudden you need a new PSU and the lower price of the 400 Watt PSU is no longer looking so good.

Peak efficiency range is around 50-80%. I don't see how a system pulling 200-250W is at that range if you put a 850W PSU.


I beg to differ, the peak efficiency of my Corsair AX850 is reached at 340 Watts (91%). That would be 40% load.

What WolfOx has in his system is already obsolete so he will be upgrading the hardware. Add in a few odds and ends - hard drive, DVD RW etc. - and the power consumption of the system rises.

I'm not saying he should get a higher rated PSU but in the discussion thus far the option was not mentioned, that's why I brought it up.
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Re: 7870 and 400W PSU

Postposted on Sun Jun 09, 2013 7:41 pm

Any bronze rated PSU or above are very close to peak efficiency (which generally occurs ~50% load) between 20%-80% load. However, below 10-15% load, depending on the PSU, is where efficiency really starts to fall off. Most current decent PSUs do very well above 80%.

Anyway, even if you pull 250W while playing games, if your computer is on 80%+ of the time idling or doing less demanding things like web surfing, etc, you'll probably be pulling under 100W most of the time. While leaving headroom for future expansion/overclocking could be a good idea, usage model should also be factored in when choosing a PSU. If you are doing CPU and GPU intensive tasks most of the time the machine is on, then any decent PSU under 1000W should give you reasonable efficiency. If you don't game or do GPGPU stuff very often, then it would probably be best to pick a more conservative PSU (ie, 400-650W, depending on config, for most single GPU systems).
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Re: 7870 and 400W PSU

Postposted on Sun Jun 09, 2013 8:42 pm

Nec_V20 wrote:Buying an expensive 80+ Gold 750 or 850 Watt PSU might seem like overkill, however in your system you will always be running it in it's peak efficiency range and will save you quite a bit of money over time compared to a PSU which will be running at over 75% all the time.

Also what happens when you upgrade your system in the future (crossfire for instance)? All of a sudden you need a new PSU and the lower price of the 400 Watt PSU is no longer looking so good.


Wait, so you're advocating the OP spend money now to buy a more powerful PSU so he can run it futher from its peak efficiency at both load and idle on the off chance that he buys a second card to crossfire on a motherboard that isn't ideal for crossfire (PCIE x16/4)? At an average electricity price of 12c/kwHr, it would take over 5 years to make up the price of an $80 PSU if he were to save 15W from efficiency with the new PSU (a very generous estimate), and that's if he were running his computer 24/7.

Somebody give that man a gold star!

To the OP: your existing PSU is fine for the 7870, no need to upgrade the PSU.
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Re: 7870 and 400W PSU

Postposted on Sun Jun 09, 2013 8:54 pm

To be fair his 400W PSU is probably putting out a lot less than that if he's had it for a while. Still probably enough for the relatively basic build he wants but could run into some issues down the road.
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Re: 7870 and 400W PSU

Postposted on Mon Jun 10, 2013 12:13 am

Wow have the forums been overrun by PSU sales reps or something? Must be a slow quarter.

Power drop for a typical PSU is ~15-20% over 5-7 years, and that's a worst case scenario. The 400CX is a well built 'value' PSU that will happily chug along for years.

On top of that, the '250W' power draw measured in the 7870 review is at the wall. PSUs are rated for 'output' power, which in this case would be 200W from the PSU. A 400W PSU is *plenty*, even with a 20% peak power drop over 7 years.

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Re: 7870 and 400W PSU

Postposted on Mon Jun 10, 2013 1:51 am

Voldenuit wrote:Power drop for a typical PSU is ~15-20% over 5-7 years, and that's a worst case scenario. The 400CX is a well built 'value' PSU that will happily chug along for years.

On top of that, the '250W' power draw measured in the 7870 review is at the wall. PSUs are rated for 'output' power, which in this case would be 200W from the PSU. A 400W PSU is *plenty*, even with a 20% peak power drop over 7 years.


Good to know. More than any other computer component, I think there is a lot of disinformation and general "mystery" surrounding PSUs that leads lots of people to make poor choices when it comes to picking a PSU.
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Re: 7870 and 400W PSU

Postposted on Mon Jun 10, 2013 3:18 am

Voldenuit wrote:
Nec_V20 wrote:Buying an expensive 80+ Gold 750 or 850 Watt PSU might seem like overkill, however in your system you will always be running it in it's peak efficiency range and will save you quite a bit of money over time compared to a PSU which will be running at over 75% all the time.

Also what happens when you upgrade your system in the future (crossfire for instance)? All of a sudden you need a new PSU and the lower price of the 400 Watt PSU is no longer looking so good.


Wait, so you're advocating the OP spend money now to buy a more powerful PSU so he can run it futher from its peak efficiency at both load and idle on the off chance that he buys a second card to crossfire on a motherboard that isn't ideal for crossfire (PCIE x16/4)? At an average electricity price of 12c/kwHr, it would take over 5 years to make up the price of an $80 PSU if he were to save 15W from efficiency with the new PSU (a very generous estimate), and that's if he were running his computer 24/7.

Somebody give that man a gold star!

To the OP: your existing PSU is fine for the 7870, no need to upgrade the PSU.


You did not look at WolfOx's spec in his original post, something which I took into account when I wrote my post on this thread.

His system is reaching obsolescence and he will obviously be rebuilding it completely sometime in the near future; and when you start going down that route you start adding things on.

If I were to identify three components one should never skimp on then they would be PSU, Motherboard and CPU. If you were to twist my arm and reduce that to two components I would say PSU and Motherboard. When I built my current machine about three years ago (it has been running 24/7 for 938 days 13 hours) I assumed that one of the first components I would need to replace was my graphics card (an XFX 5770) however that has held up pretty well to the demands I have placed on it. I got a really good deal on an i7 965x (not ES) originally and last year I got another great deal on an i7 990x (also not ES). The system now has five hard drives, two SSDs, one StorageWorks SCSI DAT 72 tape drive, a DVD RW and Blu-Ray drive running and I have between five and seven USB devices hanging off it. It also has four 200 mm fans, one 140 mm fan, and three 120 mm fans running and of course water cooling. Then there are the six 4 GB RAM modules and a few other odds and ends.

I did not plan the system that way, it grew and the overdimensioned AX850 I originally put in the machine has withstood a power surge in our house which took out the PSUs (and in one case the Motherboard) of my two neighbours living in the same house. And no, I did not have the computer running off my UPS at the time because a few days earlier we had a power cut and I used it to power my comms equipment and used my netbook (I have now got that eventuality sorted) for Internet - as opposed to Internyet - access for the time it took to get the power restored and had not switched it back. The PSU was inoperable for about 10 minutes and I feared the worst, however after having disconnected it from the mains for 10 mins and plugging it back in again the system booted up none the worse for wear.

I also have to say that in the 15 years I had computers in Germany I only had one PSU die on me (and that was most likely of old age more than anything else) and nothing else, I then moved to the UK. Before I bought the AX850 I had a total of six PSUs go nipples up here (some spectacularly) in a period of nine years and a total of three motherboards being fried.

And really, is spending more on a high end PSU with 105C capacitors (which age less and more slowly) instead of cheap 85C ones, or buying one with an eye to futureproofing redundancy and safety, a large price to pay for something so vital to the running and wellbeing of the computer?

I approached the OP with a different viewpoint from the ones which focussed on the minimum he could get away with with regard to power considerations. I don't think that merits a sarcastic Gold Star.
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Re: 7870 and 400W PSU

Postposted on Mon Jun 10, 2013 3:43 am

I don't think you should face any issues, i am using HD7970 Vapour X 3GB on Cooler master GX550 without facing any issues.
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Re: 7870 and 400W PSU

Postposted on Mon Jun 10, 2013 11:54 am

Nec_V20 wrote:
Voldenuit wrote:Wait, so you're advocating the OP spend money now to buy a more powerful PSU so he can run it futher from its peak efficiency at both load and idle on the off chance that he buys a second card to crossfire on a motherboard that isn't ideal for crossfire (PCIE x16/4)? At an average electricity price of 12c/kwHr, it would take over 5 years to make up the price of an $80 PSU if he were to save 15W from efficiency with the new PSU (a very generous estimate), and that's if he were running his computer 24/7.

Somebody give that man a gold star!

To the OP: your existing PSU is fine for the 7870, no need to upgrade the PSU.


You did not look at WolfOx's spec in his original post, something which I took into account when I wrote my post on this thread.


You're assuming things I did and didn't do on your end.

I did read the OP's specs, otherwise, I could not have known his motherboard PCIE lane configuration or his PSU make and model.

(Edited for snark).
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Re: 7870 and 400W PSU

Postposted on Mon Jun 10, 2013 4:43 pm

You're assuming things I did and didn't do on your end.

I did read the OP's specs, otherwise, I could not have known his motherboard PCIE lane configuration or his PSU make and model.


What strikes me in your replies to my post is the assumption of bad faith on my part with regard to the original poster.

If I granted you read - and understood the ramifications of - the specs and came to the recommendation you did with regard to his PSU, is it so outlandish and alien to you that someone might look at the specs and, in the light of their own experience, put forward a different consideration for the OP to take into account?

The following however tends me to believe that you did not understand the ramifications of the specs of the original poster and belies your statement above:
Wait, so you're advocating the OP spend money now to buy a more powerful PSU so he can run it futher from its peak efficiency at both load and idle on the off chance that he buys a second card to crossfire on a motherboard that isn't ideal for crossfire (PCIE x16/4)?


If the person considers his HD 5770 to be inadequate and in need of replacement then it is not a large stretch of the imagination to postulate that the person might look upon the rest of his system with an eye to replacing it. Although my own system is based on a Core i7 990x I still have the XFX HD 5770 I originally built into it as a placeholder three years ago and I am pleasantly surprised how well it has held up (I assumed I would have to replace it at the time and was waiting for the prices for the more performant graphic cards to come down). So when I read that person's specs I was pretty sure that a 7870 was not going to give him the performance boost he obviously promises himself.

You jumped into this thread not with any advice for the original poster but rather to try to stomp on someone you perceive as a newbie, and therefore weak because he has not been on this forum very long, for no other reason I can divine other than as an attempt to intimidate.

Sonny, I have been the senior escalation point for enterprise disaster recovery tech-support - I don't intimidate worth a damn.

And before you try to come back with something like, "Well I would not want to be one of the ones looking for help from you", out of the well over 17,000 individual enterprise cases/escalations I dealt with I failed to resolve exactly 223 (and I don't count kludges, workarounds or fobbing the customer off as resolutions) and in over 95% of the cases I didn't need to touch our own stuff.
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Re: 7870 and 400W PSU

Postposted on Mon Jun 10, 2013 5:30 pm

Nec_V20 wrote:You jumped into this thread not with any advice for the original poster but rather to try to stomp on someone you perceive as a newbie, and therefore weak because he has not been on this forum very long, for no other reason I can divine other than as an attempt to intimidate.


Wow, so you now not only claim to know what I did, you now know my motivations as well?*

I joined this thread to correct what I saw as poor advice and and poorly reasoned justifications. You yourself said that your last few PSUs were blown while the UPS was disconnected, yet somehow jump to the conclusion that the fault lay with the PSUs and that the solution would be to buy a more expensive one.

In addition, you repeatedly make assertions about people's motivations and intentions instead of questioning them (with both the OP and myself). Do you know that the OP wants to upgrade the rest of his system? No, you just assumed (you may very well be correct, but you didn't bother to ask).

Telling someone to buy a good PSU is good advice. Telling someone they need to buy a new PSU when they don't, isn't.

* EDIT: For what it's worth, I didn't even look at your post count when I formulated my response, so no, I didn't post to try and 'stomp a newbie'. Very little of that happens on TR, and if my post was a little too sarcastic for your liking, rest assured there was no hostility involved.
Last edited by Voldenuit on Mon Jun 10, 2013 6:15 pm, edited 1 time in total.
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Re: 7870 and 400W PSU

Postposted on Mon Jun 10, 2013 6:08 pm

I'm sure OP knows but that CX400 will be fine. I've had a Corsair literally blow up on me and there was no system damage. Heck they even bumped me up a model. Strong Seasonic built unit. An old review by Hardware Secrets shows the units efficiency at different load levels.
Nec_V20 wrote:His system is reaching obsolescence and he will obviously be rebuilding it completely sometime in the near future; and when you start going down that route you start adding things on.

Jumping to a bit of a conclusion there.
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Re: 7870 and 400W PSU

Postposted on Mon Jun 10, 2013 6:24 pm

Voldenuit wrote:
Nec_V20 wrote:You jumped into this thread not with any advice for the original poster but rather to try to stomp on someone you perceive as a newbie, and therefore weak because he has not been on this forum very long, for no other reason I can divine other than as an attempt to intimidate.


Wow, so you now not only claim to know what I did, you now know my motivations as well?

I joined this thread to correct what I saw as poor advice and and poorly reasoned justifications. You yourself said that your last few PSUs were blown while the UPS was disconnected, yet somehow jump to the conclusion that the fault lay with the PSUs and that the solution would be to buy a more expensive one.

In addition, you repeatedly make assertions about people's motivations and intentions instead of questioning them (with both the OP and myself). Do you know that the OP wants to upgrade the rest of his system? No, you just assumed (you may very well be correct, but you didn't bother to ask).

Telling someone to buy a good PSU is good advice. Telling someone they need to buy a new PSU when they don't, isn't.


Again you read, but seemingly did not comprehend, what I wrote.

Now English is my second language, but I think I was pretty clear in making the contrast between the amount of PSUs I had fail on me in Germany (one) and the amount I had fail on me after moving to the UK (six).

I have to cop to a mea culpa with regard to not buying a UPS sooner. I always swore I would get one, but then I waited to find a good offer and it slipped my mind until the next PSU blew.

I stated in my original post:
Buying an expensive 80+ Gold 750 or 850 Watt PSU might seem like overkill, however in your system you will always be running it in it's peak efficiency range and will save you quite a bit of money over time compared to a PSU which will be running at over 75% all the time.

Also what happens when you upgrade your system in the future (crossfire for instance)? All of a sudden you need a new PSU and the lower price of the 400 Watt PSU is no longer looking so good.


At the start of the thread the original poster brought up the subject of getting a new PSU and I was addressing this eventuality. Where in that reply am I telling the person that he has to buy a new one? Again, German is my native language but I think I was pretty clear - there again English might not be your native language either.

I was voicing my opinion that if he did need to buy a new PSU because his old one was not up to the job, then just moving up a small notch might be saving at the wrong end. I should have written, "the lower price of the 500 Watt PSU ...", with regard to buying a new PSU and that was my bad. But because there had been some replies to the thread and it was not something trivial like a spelling mistake I let the error stand because I thought, in the context of the rest of my post, what I was meaning was obvious.
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Re: 7870 and 400W PSU

Postposted on Mon Jun 10, 2013 6:46 pm

GeForce6200 wrote:I'm sure OP knows but that CX400 will be fine. I've had a Corsair literally blow up on me and there was no system damage. Heck they even bumped me up a model. Strong Seasonic built unit. An old review by Hardware Secrets shows the units efficiency at different load levels.
Nec_V20 wrote:His system is reaching obsolescence and he will obviously be rebuilding it completely sometime in the near future; and when you start going down that route you start adding things on.

Jumping to a bit of a conclusion there.


As I replied to Voldenuit:

If the person considers his HD 5770 to be inadequate and in need of replacement then it is not a large stretch of the imagination to postulate that the person might look upon the rest of his system with an eye to replacing it. Although my own system is based on a Core i7 990x I still have the XFX HD 5770 I originally built into it as a placeholder three years ago and I am pleasantly surprised how well it has held up (I assumed I would have to replace it at the time and was waiting for the prices for the more performant graphic cards to come down). So when I read that person's specs I was pretty sure that a 7870 was not going to give him the performance boost he obviously promises himself.


My XFX HD 5770 is actually not the bottleneck I thought it would be.

So it is not a giant leap of logic to think that the original poster will be looking to upgrading his CPU (and probably motherboard) in the near future.
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Nec_V20
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Re: 7870 and 400W PSU

Postposted on Tue Jun 11, 2013 11:30 am

Nec_V20 wrote:At the start of the thread the original poster brought up the subject of getting a new PSU and I was addressing this eventuality. Where in that reply am I telling the person that he has to buy a new one? ...
I was voicing my opinion that if he did need to buy a new PSU because his old one was not up to the job, then just moving up a small notch might be saving at the wrong end.

The OP was asking whether or not their existing 400W PSU was enough to accomodate the 7870. I think everyone here has come to the conclusion that the answer to that is yes. The aspect of buying a new PSU would only have come into play if the existing unit was deemed incapable of this task (in which case we'd have to be discussing budget).

I don't think anybody would argue too much with the recommendations you've made in general (your wattage overprovisioning may be slightly excessive...to each their own), but again, they aren't pertinent to this particular thread. I've found that the majority of people on these forums are pretty level-headed and non-confrontational. They're not out to "get you," but there is a collective effort to ensure accurate information/recommendations are being provided while satisfying the OP's specific needs. Voldenuit simply jumped in to prevent the OP from misunderstanding your posts and thinking a new PSU was required.
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DPete27
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Re: 7870 and 400W PSU

Postposted on Tue Jun 11, 2013 1:16 pm

Voldenuit wrote:
Nec_V20 wrote:
Voldenuit wrote:Stuff.
More stuff
FIGHT!


Guys, quit frightening new forum users with massively complex and almost offtopic arguments.

Is a 400W Corsair CMPSU-400CXUK/400CX enough for an HD7870?
Yes.

/end thread.
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Chrispy_
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Re: 7870 and 400W PSU

Postposted on Tue Jun 11, 2013 2:00 pm

Chrispy_ wrote:
Guys, quit frightening new forum users with massively complex and almost offtopic arguments.

Is a 400W Corsair CMPSU-400CXUK/400CX enough for an HD7870?
Yes.

/end thread.


As long as it's not an HD 7870 with a Tahiti LE chip... :P
cynan
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Re: 7870 and 400W PSU

Postposted on Tue Jun 11, 2013 2:10 pm

cynan wrote:As long as it's not an HD 7870 with a Tahiti LE chip... :P


Haha more fuel on the fire. :p

Don't worry, even the fully-enabled Tahiti 7970 only draws 285W toal system power at the wall under load. With the OP's 83% efficient PSU, that's only 237W, still comfortably within the power capability of the 400CX. So a die harvested 7870 LE/ME/XT shouldn't be a problem either.
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Voldenuit
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