You are correct @jbright, the following is stated at the bottom of the mx datasheets
POWER CABLES
1x power cable required for each MX, 2x power cables required for MX250 and MX450. For US customers, all required power cables will be automatically included. Customers outside the US are required to order power cords separately.
Darren OConnor | doconnor@resalire.co.uk
https://www.linkedin.com/in/darrenoconnor/
I'm not an employee of Cisco/Meraki. My posts are based on Meraki best practice and what has worked for me in the field.