Dude, you should never use any adapter but that specified by the manufacturer. Regradless of how long, if you plug it in and turn it on, you can damage the pedal considerably. This can usually be easily fixed, but will require sending your pedal back to Fulltone and that takes a few weeks.

Secondly, I would not recvommend a cheap power supply...you need a consistent regulated supply, or you could damage the pedal again...the pedal is designed to handle a certain voltage and exceeding that can blow components.

Rather buy a fulltone psu, they go for about 25$ and should keep it all safe.

Good luck, hope you've not already caused any problems with your new pedal.