Electronic – My robot’s motor has begun to spin slower, but it works perfectly if I use a different adapter with more voltage.. what does it mean

I have the iRobot, a ping pong throwing robot.

I've used it for years without any issues. At one point, my cats chewed out the original AC Adapter but luckily I had another one on hand from another device that had the same specs.

The power specs on the product's website list:

Includes: iPong® Robot, Remote Control, A/C adapter, Setup & Instruction manual
Input: 100-240V ~50/60Hz 0.6A
Output: 9V 2.0A


The label near the power port on the robot lists 6V --- 650mA

Now.. unfortunately I am not sure what the original Power Adapter had in terms of specs because it was a generic brand and I didn't label it. I do have a chewed up cable here which I believe was the one in question. This one lists

Output 12V DC 300mA


Does it make sense that the robot shipped with a power adapter whose specs are not quite the ones of the robot's requirements?

Now.. the replacement adapter that I had been using for ~1-2 year has this output: 6V DC 650mA

But suddenly about a week ago, it still runs but the motor is spinning a lot slower and basically it is now longer flinging ping pong balls.. it just doesn't work anymore. But it worked for a long time.. I got a lot use out of it. So this confused me.

I opened up the robot, cleaned the parts.. removing cat hair and dust.. added a little machine oil and put it back together.. no change. Now I don't have any power meter tools.. or any multi adapters. But today I rummaged through all my existing power supplies for other products.. looking for the ones that had a connector that would fit inside my robot and I came accross only one that made my robot work.

This adapter has this rating: Output 13.5V DC 1000mA

Now this one clerly seems like overkill.. although it makes me wonder since the original adapter I was using.. the one I believe shipped with the robot.. is a 12V adapter.

Using the 13.5 1000mA adapter the robot now works perfectly and is doing a splendid job. I didn't run it for more than 10 minute so far but it seems good as new.

Now I am trying to figure out which replacement power adapter I should be ordering online… one that will please my robot but without sending it to an early death.

Can anyone elaborate please?

Thanks much!!