A similar but slightly different solution to @dannybuoy, I use self adhesive cable clips like these: https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F162515629911
I find them much less hassle than cable ties as you can just push/pull the cables into and out of them easily. They come in different sizes - the smallest size can grip a couple of power cables at a time, the larger ones can hold more. Here’s a photo of the bottom of my old main board. All the clips except one are the smallest size, with one large clip which I put on to hold the actual barrel jack end of one of the cables, which it did perfectly: