Power Supply mod(s) can be found on the Mods page.
You may also find something useful in the Thingiverse Power Supply Collection.

The input side of the external power supply has a standard IEC 320 C14 type input. The cord is has a standard IEC 320 C13 type plug.
You should be able to use a standard computer power supply cable from the wall outlet to the external power supply brick.

Outer: 5.5 mm
Inner: 2.5 mm
(5.5 x 2.5 mm Connector)

The external power supply (EPS) was changed at the beginning of 2017. This was done to comply with the U.S. Department of Energy (DoE) Level VI energy efficiency requirements.

https://www.energy.gov/sites/prod/files/2014/02/f7/eps_ecs_final_rule.pdf
http://www.cui.com/efficiency-standards
http://www.metlabs.com/energy-star-2/external-power-supplies-must-meet-level-vi-energy-efficiency-requirements-for-u-s-doe-by-february-2016/
http://www.currentsolutions.com/level-vi-is-coming!-are-you-ready/

Please ensure that you purchase a 12 Volt power supply with the correct Amp rating.
Some listings have multiple products versions available on the same page.

Amazon.com - COOLM AC Adapter 12V 10A Power Adapter AC 100-240V to DC 12V Power Supply Charger with 5.5mm x 2.5mm DC Plug
NOTE: I have purchased and used this power supply. At the time of adding to the wiki I have used this power supply for approximately 40-50 hours of printing on a Select Mini V2 without any problems. The barrel plug fits the printer snugly as it should.

Amazon.ca - COOLM AC Adapter 12V 10A Power Adapter AC 100-240V to DC 12V Power Supply Charger with 5.5mm x 2.5mm DC Plug
NOTE: I have purchased this from Amazon US. See more info in the link above.

Amazon.com - SHNITPWR 12V 10A 120W Adapter AD/DC 110V 100-240V 50/60 Hz to 12V Power Supply
NOTE: There are reviews claiming the power supply is generating excessive heat. I have not noticed this with the unit I have but I also haven't bothered to check on it since it appeared to be working normally. I will keep and eye on it and update this anything changes. I will find another listing or two to purchase and test so there are more that two options listed.
NOTE: I use this power supply without any problems on both the Select Mini and Mini Delta. The barrel plug fits the printer snugly as it should.

Amazon.ca - Delippo 12V 10A 120W Power Adapter Strip Light Supply 5050 2835 LED strip 100V-240V Power Supply
NOTE: I have not used this power supply but it does match the specifications for power and the proper plug size for the printer.

Amazon.com - Winkeyes AC 100-240V to DC 12V 10A Switching Power Supply Adapter
It was reported by a user on July 3, 2018 that this power supply is now shipping with a 5.5 x 2.1mm on all outputs.
This power supply has a 5.5mm x 2.5mm connector and includes a pigtail splitter with eight 2.1mm connectors. The splitter cable is not needed. The product description refers to the 2.1mm pigtail ends.
NOTE: As of the last time I purchased on June 24, 2017 and Amazon reviews from January 2018, the power supply did ship with the appropriate size connector which is 5.5 x 2.5mm. This may not be the case any longer so I'll try to locate a suitable replacement that isn't $48.