Native instrument’s A61 keyboard

No idea if it will work. It is designed for things that need more power than the bus was designed to provide which sounds like your problem. If the problem is the port malfunctioning, it might not solve it.

I also don’t know where you can buy one. It is something like this: https://www.newegg.com/p/181-06M0-00157

But, you would need to find one with proper ends for your Mac and keyboard. That one linked has two USB A-type plugs into computer, and the USB A-type plug from the keyboard goes into the other end of the Y.

Just to add, if you are plugging the keyboard into a USB hub or adapter try plugging it directly into a USB port.

Good idea, and I'll add an alternative that you reminded me of. Maybe use an externally powered hub instead of the Y-cable.

However, I've seen where some things don't work well through a hub.

Then try a powered hub, if you have one. That might solve the over-current problem.

You might try a Y-cable which connects to two USB ports. It runs power and data on one, and also draws power from the other port.

Just to add, if you are plugging the keyboard into a USB hub or adapter try plugging it directly into a USB port.