I have Irritrol case which comes with a 24V transformer and I would like to reuse this case. So my question is if I use that 24 v transformer to power the OpenSprinkler and a 24V to 5V 3A Step-Down USB Output Converter in order to power the TP link Wifi device it should work? It should be more than enough voltage to handle both items.
Because OpenSprinkler has a USB port which can supply 5V to power an external device, you can actually use this adapter: http://rayshobby.net/cart/accessories/acc-usb/usb-fa-mb
to power TP-Link from OpenSprinkler’s USB port.
A separate 24V to 5V step-down converter is also fine.