@overeasy following your post I’ll do some tests before I install the socket.
Doesn’t seem to be an issue. Had the AC - AC, small Android phone charging and ESP8266 running without any problems.
The big thing to look out for with cheap 5V USB supplies is ripple, if that 5V source is your ADC reference voltage. If you have other voltage regulators between the 5V source and your ADC reference then you need to check their ripple rejection capabilities.
Just to add a different prospective, I have wired a 12v supply from my intruder alarm, this has the added benefit of not only containing the extremely small DC to DC converter in the adaptable box but it is effectively a UPS (Battery backed up system) for my system.
Regards
Dave
Very sneaky. 
I am new to Open Energy Monitor and I am very excitied to find you!
I was looking at the arduino energy monitor and the article spoke of powering the device with a battery. I would like to avoid batteries, espeicially if I have power right there. For my Arduino/ESP projects I’ve been using inexpensive/cheap power supplies. The input for these are AC50V-277V DC70V-390V so they can be used pretty much anywhere.
The current measurement is isolated. Using the AC to AC power adapter (aka transformer) isolates the voltage measurement.
My question is, do you see any safety issues using the aforementioned power supplies?
I’ll be looking at the ripple on the power supply output.
Thanks for your input
OSD
Welcome, Gregg, to the OEM forum.
I’m in the UK and I have no experience of those particular units. However, at that price, I would be EXTREMELY cautious, because economies must have been made to achieve that selling price, and cheap and possibly unreliable components is an obvious place.
I’d be looking at clearances between the input and output, and the voltage rating of the components on the mains side of the isolation barrier.
I have popped mine into the same cupboard as the network kit (router, switches pihole etc.)
It is powered via POE and a POE to micro usb dongle and seems to be running quite well for over 7 months now.
Not an option for everyone I know but was a quick win for me as I was a bit limited on mains connections.
@Robert.Wall I agree with your concerns and not to be taken lightly. In fact, the first time I turned one one, I put a fused switch and a piece of wood between me and the unit 
. My experience has been good, but I may be lucky.
Actually I was trying to ask if such a design, powering from the mains knowing that all the inputs are isolated, is a good idea. Of course, assuming that the power supply was of good design and manufacture, though ground may be connected to the mains in some way.
I would send the data wirelessly, using an nRF24 radio, thus isolating it from the data network (see MySensors)
Thanks for your input
OSD
If you can show that the COM/GND/zero volt rails is truly isolated to both d.c. and a.c., then I’d bond that to your protective ground just in case anything went seriously wrong.
I don’t know what the rules are where you are, in the UK there’s nothing wrong with isolating the inputs, and without this, you’re into all sorts of trouble meeting safety requirements if you offer it for sale and even if it’s your own home, your insurance company might ask awkward questions if they’re faced with a big payout if something goes seriously wrong. If you didn’t isolate the inputs and had the output via radio, that’s OK but you then need an earthed metal or a totally insulating enclosure, and you’d be at risk working on it.
If you can, I’d still ground the common side of the low voltage supply. Without this, you are more likely to pick up interference etc in the measuring circuits.
With an abundance of caution, I did the experiment. I connected 240AC to the input and connected the GND of the output to earth ground. From GND to VCC was 5VDC. No magic smoke released.
In the USA houses are delivered 240VAC single phase with a neutral. Thus two legs of 120VAC (if you don’t load one of the legs too much.) The neutral is grounded both at the distribution transformer and the house mains (panel). At a wall plug you will find Line, Neutral and (earth) Ground. Sometimes you will find ~85VA between Neutral and Ground, but this indicates a poor earthing at the panel. While I’m an electrical engineer (retired) I have never understood why this works, but it does.
What I have shown is that this power supply will work to power an energy sensor as described on this website. @Robert.Wall, you correctly indicate that doing so runs a lot of risk. (Here in the USA, insurance companies often refuse to pay out on claims because they know the insured is too poor to hire an attorney.)
I agree that connecting the common of the low voltage is a must, for safety and noise.
Speaking of noise, I measured the ripple and it’s pretty ugly. 20mV p-p. The dominate frequency varies with load, 800Hz at no load, 33kHz at 400mA. There are a lot of harmonics and outright noise, too. Despite that, I am powering an ESP-12F which connects to my router via WiFi.
I’ll just have to build an energy sensor and see if it works. I’ll be using an Arduino Nano.
I appreciate your input @Robert.Wall !
OSD
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You might like to look up this very old post about 5 V power supplies. Things might have changed since, but quite possibly not.
Bad USB Power Supply: Not all USB power supplies are created the same - Blog | OpenEnergyMonitor
And another old discussion that could be of interest:
Noise in Arduino-based builds: Noise in Arduino based builds. | Archived Forum