You may want to try the soft side of a small strip of self-adhesive velcro. When I first purchased my 2k I used it to attach the power pack to the back of the keyboard. Unfortunately, when the power pack warmed up, the adhesive gave way and the pack dropped on the floor--not a good thing to happen in the middle of a song. Sure wish Yamaha would go back to built-in power supplies.
Good Luck,
Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)