EcoFlow Customer support got back to me, Delta Pro's can not be connected together and used in this configuration
Now I got another response saying it is possible. For those who might be interested:
Thank you for contacting EcoFlow support.
Here is the series mode user guide for Daisy chaining two Delta Pro together (Recommended for power users; all machines must be fully charged).
Users can connect two fully-charged EF DELTA Pros in series using the AC charging cable to get continuous power and supply appliances.
In this mode, do not connect EF DELTA Pro to the power grid using an AC charging cable, or the overcurrent protection may be triggered.
Connect EF DELTA Pro to a home power grid and charge each EF DELTA Pro separately.
It is not recommended to charge more than two machines simultaneously. Otherwise, the excessive load may cause damage to the home power grid.
To use this function, you need to first set any of the machines as the master and the others as Slave 1 and Slave 2.
Connect one end of the AC cable to the AC output port of the master unit and the other end to the input port of Slave 1.
Then, connect one end of the AC cable to the AC output port of Slave 1 and the other end to the input port of Slave 2.
After connecting the machines, turn all the AC switches on to activate the multi-machine series mode.
Finally, connect all the appliances to the AC sockets of Slave 2 and then you can charge your devices using EF DELTA Pro and enjoy the benefits of extended powering time.
