Making an adapter to run your 9V powered Bleep Labs device off a DC power supply is easy. This guide is based around using a standard 9v stompbox power supply like this one but any 9v DC power supply what is center negative and rated of at least 200mA could be used.
You can also use an off the shelf solution like this

1.

First, you’ll need a 9v battery clip and a female 2.1mm DC jack. I recommend using a hard plastic battery snap since the soft ones can get stuck in the device’s battery holder.

Here’s parts I used from Mouser : Battery snap DC jack

2.

Unscrew the plug’s plastic housing and put the wires through as shown.

Stompbox power supply plugs are positive on the outside and negative in the middle. This mean that the lug from the center should connect to the red wire and the lug for the outside should connect to the black wire.

After it’s all soldered up, cover the small lug with electrical tape and use some small pliers to crimp the longer lug around the wires.

3.

With everything soldered up, make sure the wires aren’t touching and screw the housing on. Connect the adapter to the battery holder, plug up the power supply, and turn the device on. If nothing happens IMMEDIATELY turn it off and unplug the DC adapter. Check your polarity and make sure the wires aren’t shorting out.

4.

For the Thingamagoop, you can use diagonal cutters to make a small notch on the battery door. Be sure to keep the battery connectors inside the battery compartment.