Constantly tripping GFCI

I have a device that’s constantly tripping my GFCI outlet even when it’s turned off. It will trip it immediately upon plugging it in. This is in the US. The outlet is on a circuit with only one other outlet and nothing else plugged in. The device is connecting over a standard 120v power cable and its own plug is rated at 10a/250v. This is the second device I’ve tried since I originally thought the first was defective. What could cause this? What could I do to fix it? What should I look for for further diagnosis?