Which brand of Smart Plugs are the right size? I have one, but it is so bulky, I can only use one outlet of the double-outlet. That seems to be a waste of space.
I am not sure why they don't make them in the right footprint, so you can still use the other outlet.
I've got both Leviton and Minoston plug-ins that don't block the other outlet.
Answer depends on the type of outlet (since we are international). In US/Canada, the standard 110 V outlets with two plugs have a wide choice.
In addition to Joe's plugs, the Kasa Smart Plugs are compatible with Hubitat using the built in integration application. I usually search on Amazon the buy locally. Example (from US Amazon search):
Caution: as you do searches, make sure bargain items are supported by Hubitat. For example, the Amazon brand plugs are NOT compatible with Hubitat while the Kasa brand are.
Detailed as always.... and here I thought I had a simple / popular answer... 
Dave's right... take note of what is supported in your location, regardless of the tech involved.
You beat me. I just was not aware while I was creating.
Being retired, I have time to formulate detailed answers. Nothing but time.............
One day.... One day.... Don't stop the detail, helps fill in the gaps for us time-poor workers
I am in the US
I'd steer away from the power monitoring versions as well, unless needed.
They add more traffic on the mesh, that you might not be able to suppress, and they could be subject to erroneous self-protection shutdowns.
That's possibly true, and would make sense to me, but would it be best to assess that on a device by device basis? The Kasa devices have certainly served me well, admittedly poll-based, but still rock-solid, and configurable for the polling period, which I make use of....
Aeotec Smart Switch 7, Z-Wave Plus S2 Wireless Control Socket Zwave Plug for Home Automation, 15A, Gen7, White https://a.co/d/2JAckpx
Not cheap, but I like these.
As long as you get the right models, the TP-Link Kasa plugs are supported. But they are WiFi plugs that have a community driver for use with Hubitat.
I much prefer Zigbee plugs as they also function as Zigbee repeaters. In the past, I have used the eWeLink technology 10 amp plugs such as the ones by CMARS. However, after a couple of the plugs failed during a recent power outage caused by an electrical storm, I replaced them with the 15 amp plugs by Third Reality. If you get the 4-pack, they are inexpensive. They do not block the second outlet.
https://www.amazon.com/dp/B0BPY5D1KC/
Third Reality also makes a Gen 2 plug that has power monitoring. However, these devices generate a lot of traffic on the Zigbee network. Thus, I would recommend that you only use them if you have a specific application requiring power monitoring.
These smart plugs are suitable for resistance loads only up to the rated maximum. If you are monitoring a 110V load that has a motor, these are not suitable. I am using the Zooz Zen15 Z-wave smartplugs to monitor devices like my clothes washer, gas dryer, and sump pump. They are rated at 16 amps and can handle the startup load of small motors. The Zen15 is not nearly as compact as the Zigbee smartplugs.
However, you can completely turn off reporting and they seem to be more resistant to erroneous shutdowns.
Zooz just came out with a firmware update for the ZEN04, 1.30, that allows you to just about turn off all reporting except for Energy use, which is a max threshold of 1 kwh.
The update also has a faster reporting of zero power; 5 seconds vs 35 seconds.
I like the auto/on and auto/off timers as well as their adjustable post-outage behavior.
@jtp10181 's Zooz plug driver is very handy and flexible as well. There is an 'accessory' setting, such that anything below a certain wattage, say 5 W, is considered 'off'. He also has the option on the device page to adjust parameters, which thus can be accessed with a rule.
The latest changes with 1.30 can be adjusted in his driver without being affected by a parameter save, since Zooz created new parameters.
I have used Innr SP 224 and Centralite 4200-C plugs with good success. They are small enough to only take up one outlet on a duplex receptacle. They are Zigbee plugs and also make good repeaters.
I was going to recommend the Sengled Smart Plugs I have around my house, but I see a 4 pack is now nearly $80!
I like them, but not $20/piece like them.
The reason I have the Zen15 plugs is to monitor energy usage on my washer, gas dryer, and sump pump. I do not use the plugs to turn power off and on. They do serve as Z-wave range extenders, but that is not why I got them.
These 
But I like the Centralite better as you can have two on one outlet if you want. Centralite has been in the HA business forever and makes quality products.
Also like the Sengled, can also put two on one outlet.
The Centralite 4200-C plugs are HA 1.2 certified, not Zigbee 3.0 certified. I have a couple of the Centralite plugs in my spare parts bin. I initially removed them from my mesh when I tried installing a couple of Aqara devices on my C7. The Aqara devices would not stay connected as long as the Centralite plugs were in the mesh. I had to remove my Smartthings HA 1.2 plugs for the same reason.
As long as you do not have Aqara devices, the older Centralite plugs might work well. However, i now have an abundance of Zigbee 3.0 plugs, so I do not plan to reuse the older plugs.
Since upgrading from C7 to C8, I have not been able to get my Aqara devices to work. They have since been replaced with Zigbee 3.0 certified devices since Aqara is non-standard and not guaranteed to work with Hubitat, although some people have gotten them to work.
I just asked in another post if it is worth it to upgrade from a C-7 to a C-8. Is it worth it?
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