I have a cheap thin battery bank that only does 15w.

With that in my back pocket, and a cable to the back of the head, I can play beat saber, and while it definitely doesn't charge the frame, it slows its drainage to a handful of percent an hour. Which is fine for me, the whole setup is so light you don't even notice it.

This is my first time with VR of any kind so take that with a grain of salt.

Edit: I went and checked with a meter. It's only providing 4.6v at a little over 2.5 amps. So just under 12 watts. Not a lot for this thing!

I also watched the drain closer, it's more like 20 or 25 percent per hour. Which isn't great, like 4 hours runtime instead of the 1.5 or 2 they said you could get?

But, I have yet to play for more than a couple hours at a time, so this is more than enough. Eventually I'll upgrade to a thin pack that can do more, I really don't think it'd take much to get this thing running for hours and hours, yet not drag your pocket down.

The point still stands, you don't need a giant PSU to get usable performance.