Condensatior problem

Hello. In my project i have a 12v Wenglor sensor. This goes to a regulated power supply thats shuld convert the 12v to 5v. And then i connect the signal to a velleman I/O-Shield on a digital input.

But when my sensor goes LOW the condensaitors on the power supply seems to keep allot off the power for a long time?

What can i do? Is my setup incorrect? (see attached image)

Wenglor yh08pct8;;wec-appid::Shop_1000_EXT_EN;;wec-locale::en_US;;itemKey::YH08PCT8;;ifr::y

Regulated power supply 5V & 12V 1A

Velleman I/O Shield

It seems you're trying to use a switching (buck) power supply to drop the 12volt output from the sensor to 5volt for the shield/Arduino.
Not how it's done, and dangerous for the Arduino input pin. Don't use.

Connect 12volt directly to Arduino's DC socket.
(That relay shield needs 12volt (12volt relays), and gets it's power from Arduino's V-in).

Connect the sensor (power) to Arduino's V-in (+) and ground (-).
You might have to solder a wire to V-in for +supply.
Ground is available on the screw terminal.

Use a 10k resistor from an input pin to Arduino ground.
Use a 15k resistor from that Arduino input pin to sensor output.
That will safely drop 12volt from the sensor output to ~5volt for the Arduino input.

Arduino (Uno) + relay shield + sensor will use about 250mA, so use a REGULATED 12volt/500mA supply.
Don't use that ancient technology linear supply board that you linked to.
Get a switching (universal mains voltage) 12volt/500mA plugpack.