Jameco Reliapro ACU120100D0531 AC to AC Wall Adapter Transformer 12V @ 1000 mA Straight 2.5 mm Female Plug, Black - 100167

Try a new transformer first. I know you said it reads 12v with a multimeter but it may not be able to supply enough current to operate the controller. It's a very common power supply. 12vAC, 500mA (or greater). Look around the house you might have one for something else that you can try. Or this one should work https://a.co/d/05K4Qajf