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XPS 8900, AC Recovery not working, replacement PSU
Hello all,
2 months ago, I replaced the stock PSU on my 2 years old XPS 8900 with a Seasonic 550W (ref. SSR-550PD2). This new PSU has a bit more oomph on the 12V rail (up to 540W instead of 385W), in anticipation of an upcoming GPU upgrade. It fits perfectly (the size is exactly the same as the Stock PSU) and it's silent.
However, one thing puzzles me. Not a big issue but I'd like to understand if this is an indication of a faulty unit?
In the bios, I like to have power management "AC Recovery" set to "On". It allows me to start the PC from the power strip, without having to press the power button. After I installed the new PSU, this doesn't work 100% of the time anymore. Once, my PC started to boot momentarily, then turned off. On a few occasions, it did not boot at all. When I press the power button afterwards, it works every time.
I've been trying to find a pattern. Here is what I found:
- When I switch the power strip off, wait less than 2 minutes, then switch it back on, the PC won't boot. However, when the power is turned off longer, then turned on, it boots most of the time.
- When starting the PC from the power strip, with the PSU, I don't hear the fans speeding up during boot sequence anymore. I do hear the fans when I start the PC from the power button.
Other than that, the system is perfectly stable. What do you think about this behavior? Is that common with a replacement PSU?--
EDIT : thank you all for your answers! I guess the new PSU takes longer to fully energize, compared to the stock PSU. It could be in fact a trademark of a higher quality PSU. I'll give up on powering the PC from the power strip from now on...
Vic384
1 Rookie
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3.2K Posts
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July 6th, 2018 17:00
I think the behavior you are describing is reasonable given that parts of a power supply are normally energized (like the circuitry that monitors the power on/off signal) when AC power is applied even if the PC if off. By cutting off the AC power, those parts of the power supply that are normally energized may not be full energized once AC power is applied and power is demanded. Personally I would discontinue this practice and apply AC power then wait before turning on the PC, in other words set AC Recovery to Off. DC power from the power supply is not instantaneous once AC power is applied, and varies from one power supply to another. Power supplies do not energize fully instantaneously and they also do not de-energize instantaneously.
Tesla1856
8 Wizard
8 Wizard
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17K Posts
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July 6th, 2018 19:00
1. My guess is PG-Signal (Power Good) is too late
2. It should turn-on and boot 100% of the time
RoHe
10 Elder
10 Elder
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43.5K Posts
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July 6th, 2018 19:00
That's because the power hasn't drained out of the capacitors on the motherboard in those first 2 min so the system hasn't noticed there's been a "power failure". If you switch the power strip off and then press/hold PC's power button for ~15 sec, and then power the strip on again within those first 2 min, I bet it will boot automatically every time.
Could that be because the system is "balancing" the load, at least until the capacitors on the motherboard get charged fully and temp sensors start reading?? And by that time the video driver has loaded which have an impact on fan speed.
I've been using a power strip with my Dell desktop the same way you do for eons and it hasn't had any adverse impact. (This PC probably should be in a museum, it's so old!) But I've never had the PC not boot when I energize the power strip. So I don't know why yours doesn't, unless maybe the motherboard battery is old and weak.
Tesla1856
8 Wizard
8 Wizard
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17K Posts
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July 6th, 2018 19:00
Agreed.
And if desktop is connected to a good UPS-Battery (like APC LCD-Model) ... as it should be ... it would never been turning-off un-expectantly anyway.