I am using a RPi to switch a relay on and off at certain times of the day. I have an electric motor connected to the relay and would like to use an external 12V DC power supply (wall wart) that I have lying around to drive a 12V DC motor. I have measured various 12V DC power supplies and all of them show >12V: The nearest was 15V and one was 21V. Is that normal? More to the point is it an issue for the motor? LMK if I need to provide more info.

 

These are unregulated power supplies. They will drop to something closer to the rated voltage at the rated current.

What is current draw of the motor and the ratings if the power supplies?

 

This is the motor and peristaltic pump: https://www.amazon.com/dp/B01IUVHB8E?psc=1&ref=ppx_yo2ov_dt_b_product_details

From that page:

• Volts: DC 12V
• Current: 80mA
• Relative humidity <80%
• Temperature: 0-40℃
• Flow rate:0-100 ml/min
• Rotate speed:0.1-100 rpm
• Motor RPM: 5000RPM

The Power supply is from an old Netgear router: Output 12v 1A and says it's a Class 2 transformer.

 

They must be older style Wall-warts as typically they were unregulated, unlike modern versions which now tend to be.
Motors are typically not precise devices when it comes to voltage, you should be able to get away with the 15v which typically will drop under load.