Keep light equipment from tipping up from cable weight?

Double-faced tape on the feet, zip ties (in a range of 'attractive colors'....

I've a couple of items that suffer from the noted, but have been able to tuck them under or behind cables that keep them stable...

...and there's always Blu-Tak....

Gift wrap a brick....

I just put a box of ammo on top.  Heavy and dense, they keep everything in it's place.

A chunk of whatever is lying about wrapped in electrical tape. The tape prevents unwanted scuffing of the equipment.

There are a variety of colors of electrical tape available for those with O.C.D.

Blu-Tak is my Blu-Tak is my go-to. Other brands can leave an oily smudge or damage the finish of the component below. Gorilla double-sided tape works well and is much grippier, but also pretty close to permanent. 

Mitch2 #2 is what I use. A similar alternative is moving the component forward on a shelf so the cord is supported by the length of the shelf behind the component.