I have a device that requires input of 12V DC with positive polarity and a power supply that outputs 12V DC negative polarity (see figures below). Can I plug it in to try to see if it's working or will that harm the device?

I have a device that requires input of 12V DC with positive polarity and a power supply that outputs 12V DC negative polarity (see figures below). Can I plug it in to try to see if it's working or will that harm the device?

Using the wrong polarity will very likely damage the device, if it is polarity-sensitive. If the device has reverse-polarity protection, it won't work, but won't be damaged.