Powered USB Hub goes in and out????

Hi Everyone,

So let me start off with my setup.

I have an iMac that is a year old running the most current OSX.

I've recently had some problems with my powered usb hubs going in and out with power. So what I mean is that the external power to them seems to shut off and on at times.

I have 2 hubs connected to my imac because I have a lot of devices connected to the computer. I have a printer and scanner for my graphic design stuff and a ton of midi controllers.

I have a keyboard, 2 korg nanos, audio 8 dj, maschine, vci 100, kontrol x1, and a usb mic. I also have an apc40 but i don't leave that one plugged in.

Does anyone have an idea of what is going on. I've had this setup for a minute and didn't have any problems until recently. I also like to have my studio all setup instead of pulling out controllers and plugging them in, which is why I bought 2 hi quality kensington powered hubs.

Thanks.
Priscilla