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ShardsOfNarsil

ShardsOfNarsil

Jun 18, 2025
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Hello all, newbie here. I've got a HP system with limited expand-ability, with the psu and graphics card being part of that limitation. The psu I have is only 250W and the maximum psu I can get for the system is 400W. From the manual for the system the best video card I can get for the system is the RX 580, which the 400W is less that minimum depending on what source you read. Now the possible dumb question is can I use an additional external mounted psu, which I have a 700W from an old system, to power just the video card? There would be no connection from this external psu except to the video card's 6-pin connections. Be gentle...

Mike

PS:Obviously the 700W psu does not have the correct dimensions and connectors to mount to the system...
 
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ShardsOfNarsil said:
Now the possible dumb question is can I use an additional external mounted psu, which I have a 700W from an old system, to power just the video card?
Click to expand...
Short answer:
No

Long answer:
Well, sort of. But it carries a SIGNIFICANT risk of blowing the thing up.
And depending on the rest of this low end office type system, you may not see any real benefit in the case where you do not release the magic smoke.
 
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Well, the RX580 is certainly not the most up to date GPU you can put in there. Something like the RTX 3050 6GB would drop right in without the PSU upgrade.

Getting the 400W unit in place leaves room for things like the RTX 3060 or RX6600 depending on physical constraints.

External power supplies are a thing you can do, it isn't the smartest thing though. It is more than just plugging in the PSU to the card. Ideally you connect the grounds up, and you connect the standby wire from the HP PSU to the external PSU so that it turns on when the system is turned on. Otherwise you have to connect the standby pin yourself and make sure the external unit is running before turning on the HP.

ShardsOfNarsil said:
So would it because there would be too much power going to the card since nothing is being distributed to the mobo components?
Click to expand...

No, components only draw what they need. There is the potential differences in the 12V output of both units. But mainly that may just lead to stability issues. The other big one would depend on the type of the PSU being used. Older units rely on the 5V and 3.3V having a load, GPUs power cables are only 12V, so those PSUs can behave badly and output too high a voltage. New PSUs don't have this issue since they tend to use DC-DC converters to get the lower voltages.
 
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Eximo said:
Well, the RX580 is certainly not the most up to date GPU you can put in there. Something like the RTX 3050 6GB would drop right in without the PSU upgrade.

Getting the 400W unit in place leaves room for things like the RTX 3060 or RX6600 depending on physical constraints.

External power supplies are a thing you can do, it isn't the smartest thing though. It is more than just plugging in the PSU to the card. Ideally you connect the grounds up, and you connect the standby wire from the HP PSU to the external PSU so that it turns on when the system is turned on. Otherwise you have to connect the standby pin yourself and make sure the external unit is running before turning on the HP.



No, components only draw what they need. There is the potential differences in the 12V output of both units. But mainly that may just lead to stability issues. The other big one would depend on the type of the PSU being used. Older units rely on the 5V and 3.3V having a load, GPUs power cables are only 12V, so those PSUs can behave badly and output too high a voltage. New PSUs don't have this issue since they tend to use DC-DC converters to get the lower voltages.
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I am going off the manual for the system which lists the RX580. Granted its an older system and the manual reflects that but I am also on a severe budget restraint, so new video cards are out from the get go. I did experiment and put my old R9 270 card in but the system did not like it. Beep alarms and the fans on the vid card didn't move. I took this to mean the psu couldn't supply the power and figured the newer cards would be more demanding. You're saying the 250W psu would power the RX580???
 
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ShardsOfNarsil said:
You're saying the 250W psu would power the RX580???
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I am not saying that.

RX580 is a 185W part. That would leave practically nothing for the rest of the system.

R9-270 is a 150W card, not much better.

Something like the RX560, maybe. AMD doesn't have much that is modern on the low power front. RX5300 is barely a card at all, but qualifies.

RTX 3050 6GB is a 70W GPU, a bit pricey new, but you might be able track one down used. The older RTX 3050 8GB is only 115W, and might work as well.

Also cards like the A2000 another 70W card, which is a workstation card, but is effectively an RTX 2060. These are somewhat hard to track down, but were the go-to SFF GPU before the 3050 6GB came out.

That is all cards that fit within the 250W limits, barely. Most of those don't require supplemental power, but you would have to confirm that the PCIe slot is capable of the required 75W output. Some OEMs limit the slot power to 35W.


If you do get the 400W PSU upgrade, then yes, the RX580 becomes an option (though it was well known for drawing a lot of slot power). But it is starting to slip out of driver support.

As well as anything in that 150-180W range. GTX 1080, GTX 1070Ti, GTX 1070, all of the GTX 16 series cards, RTX 2060, RX 6600 (as mentioned before), older RX 5600.
 
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ShardsOfNarsil said:
Hello all, newbie here. I've got a HP system with limited expand-ability, with the psu and graphics card being part of that limitation. The psu I have is only 250W and the maximum psu I can get for the system is 400W. From the manual for the system the best video card I can get for the system is the RX 580, which the 400W is less that minimum depending on what source you read. Now the possible dumb question is can I use an additional external mounted psu, which I have a 700W from an old system, to power just the video card? There would be no connection from this external psu except to the video card's 6-pin connections. Be gentle...

Mike

PS:Obviously the 700W psu does not have the correct dimensions and connectors to mount to the system...
Click to expand...
What is the model of your HP? can you send us a link to the manual your looking at?
 
USAFRet said:
Right.
And trying to turn this low end proprietary office system into a semi game system never works well.
Click to expand...
I'll tell you this, its impressing the crap out of me so far. Even before increasing the ram. Upgrading the vid card and psu is a cheap way to go for me and as long as it handles the graphics, some gaming, Photoshop, etc., I throw at it, which it has so far, that's all I need.
 
What is the realistic budget constraint? Given the age of the system, you might do far better to find a dirt cheap motherboard that isn't proprietary and move the CPU/RAM to it. You could then either set it up as a test bench outside the case or get a really inexpensive case. Would have to know what the 700W PSU is, too; don't want to recommend you doing something that will make your RX 580 have a quick trip to the afterlife.
 
DSzymborski said:
What is the realistic budget constraint? Given the age of the system, you might do far better to find a dirt cheap motherboard that isn't proprietary and move the CPU/RAM to it. You could then either set it up as a test bench outside the case or get a really inexpensive case. Would have to know what the 700W PSU is, too; don't want to recommend you doing something that will make your RX 580 have a quick trip to the afterlife.
Click to expand...
I'm done doing mobo builds as that's basically all I've done up till now. I've already nixed the plan for the external PSU. For the roughly $300 total that I'm putting into the system when all is said and done, it will do what I need it to.
 
I never heard of that kind of limitation on the power of the PSU you can put in a system. Unless the slot in the case is too small to fit the unit, anything you put there should work just fine. Considering also the CPU, i'd say the system is 6-7 years old so the manual is completely outdated on the info it provides about compatible hardware. It recommends a RX580 because its probably the latest card at the time it was made, but if you have an adequate PSU and the card is not bigger than the case, you can put anything you want in there.
 
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