I guess, first you should make sure that your connections are as they should be,
Don’t see a GND on the LEDstrip in the picture, but there is a DC+ , so the R,G.B,W wires are pulled-down by the dimmer.
If your LED-strip has only 2 wires, V+ and GND, then V+ must be connected to + voltage on the power supply and the GND from the LED_stip connected to the “White” connection of the dimmer.
It is very important to have a very stable power supply, maybe an extra capacitor could help.
