@jg I'd suggest you just give it a try. I've been waiting for the Ninjas to start selling spare PSUs so that I can keep one for travelling, but it's not happened as they've been rather busy 😀
Like many people, I've got a big box full of miscellaneous computer, audio and video cables I've accumulated over the years. I went through my box and found what appeared to be the nicest-quality USB cable in there, chopped off the mini-USB end, and soldered on a Slice power connector.
The wire wasn't the thickest, but after trying it (power from a battery pack) it works fine. The Slice is quite happy and stable, and nothing even gets warm. This will allow me to use Slice on the road without having to extricate the original PSU from behind the telly!