The Problem was the serial to ethernet server(brainbox) the power supply was connected to had the serial ports set to telnet protocol type, while looking for a solution on the brainbox webside:

https://www.brainboxes.com/product/ethernet-to-serial/db9/es-701

I checked their debugging video for c# and there they set the serial ports protocol to Raw TCP, after this setting was changed I was able to get the response from the power supply.