A raspberry Pi costs up to 1€/month in electricity to keep running as a server, while any used computer will cost quite a bit more. When suggesting old hardware for server use, make sure to consider the total cost, not just the cost of the hardware itself.
It's just the top, not how low it can go on idle. My VM server has ~35W TDP but gets 20W with SSD/dual NIC and acting as WiFi accesspoint. CPU usage is less than half of that, at those levels motherboard is often the element with highest power consumption and it is hard to get data on which motherboard is most power efficient.
Probably easier with laptops as in theory you can just get run time on battery, battery size and calculate power usage off that.
I actually bought a Lenovo M910Q with i5 6500T, 256GB SSD and 8GB of RAM for ~£100 in the last year.
It'll absolutely demolish a Pi 4 at CPU & GPU performance, can take much more RAM than a Pi, idles at <10W on 230V mains, you get the bonuses of easy software compatibility as it just runs any mainstream Linux distro & and it runs x86_64 code, it has real storage interfaces (SATA & NVMe), and has an Intel NIC.
For home server uses, they're really nice machines.
Some people use power banks for that, but that's not really proper use and some power banks don't allow seamless power switch.
There are also few simpler ones that do "just" supply power and "power good" signal.
There is also plenty of DC UPSes, although often targeting the industry, which means "expensive"
In-between is [2] OpenUPS but I didn't used it. It's just pretty niche product and niche is also one of the "it will be expensive" keywords.
Soo yeah, they are out there and work fine, go and buy one. Oh, don't want to spend more than rPi ? Well, that's the price of niche products, even if parts are not super expensive it need to cost enough for NRE costs to amortize.
Or, slap a power strip and few power supplies into normal UPS and call it good enough
It has an important caveat though: both the USB and 12v outputs are unregulated, so the device you're feeding into must be able to handle a wider voltage range, or you can buy a fairly cheap ($15 or so) step up/down converter to put in-line with it.
I'd really like an affordable 5v/12v UPS though. Maybe it will happen when more things adopt USB-C and there's more of a market for power banks designed for seamless switching.
In place of them, I got a barebones Intel Nuc that I populated with some DDR4 and an M.2 NVMe drive I had laying around. The performance from the Core i5 is great and leaps ahead of the most powerful Pis, and the footprint and cost is only a little more than a fully heatsinked and encased Raspberry Pi. My Intel Nuc is running Linux Mint flawlessly so far.
https://www.amazon.in/Intel-Core-Mini-NUC8i5BEH-500GB/dp/B07... (INR 52K or US$ 600) https://www.amazon.in/Intel-Performance-NUC11PAHI5-Thunderbo... (INR 42K or US$ 488)
or you can get a celeron https://www.amazon.in/Intel-NUC7CJYH-NUC-Kit-BOXNUC7CJYH/dp/... (INR 12K or US$ 139)
https://robu.in/product/raspberry-pi-3-model-a-with-official... (inr 2800 or US$32)
or https://robu.in/product/raspberry-pi-3-model-a/ (INR 2500 or US$29)
so the NUC are being sold at obscene prices....
i am very much interested in buying old tech because
1. it is cheaper and has seen a lot so it usually isnt flimsy. 2. no need for warranty as the local repair scene is pretty good with aftermarket spares readily available.
i broke 4-5 Pis last year because of a bad usb cable that was transferring data and i didnt realize until later the cause. anyway, i am stuck with pis with USB overcurrent problem.
A question I keep asking is what happened to the cheap NUC's?
This question has been bothering me since the $199 J1900 NUC disappeared years back and was never replaced by a comparative low power and low cost NUC. Instead we got $400+ i3/5/7 NUC's and some silly $1200 NUC with a skull on it for gaming. They were at one point cost effective but that suddenly stopped.
Few weeks back I picked up an i5 NUC on sale for $300 from Newegg which is the lowest I've seen a quad core NUC in a long time (maybe I'm not looking hard enough). It's hooked to my TV and is just another desktop that also happens to play Hulu.
If you don't mind buying used, the prices drop even further.
Ironically, I'd be happy to pay much more than the cost of a entire Pi4 to get the same GPIO as an add-on for a fast, reliable amd64 machine.
I for one run a Pi with PiHole, Wireguard, Unifi controller, NVR, MQTT, etc. and a few more GPIO trinkets like Zwave. No ESP could practically handle all that, an x86 would be overkill in terms of size, noise, temperature, and power consumption.
On the other hand I use ESPs for things like "smartening up" my door intercom where even a Pi Zero would be overkill.
You probably would be surprised what they can handle... See these examples:
I must have a lower tolerance than most, but the idea of typing on a used keyboard seems gross. Besides, how do I know how well was it handled? That the power supply will not fry a few weeks in, just after I set everything up.
I have a Raspberry Pi running nonstop for over a decade. No fans, just working.
First party refurbished are usually as good as new.
It takes up more space, and uses more power, but no paying scalper prices for hardware dependent on a dodgy microSD, wallwart, USB SATA adapter, improvised chassis, etc.
Better than buying brand-new perhaps but not what I would call a great deal and certainly not a replacement for a pi4 in terms of price and power consumption.