Assuming that everything involved with driving the LOTR magnet is 100% efficient, then those formulas work (ie 5a * 50v). Since there is no way that's true, it can't hurt to be safe in adjusting the calculations 'up' a bit. I have a meanwell switching power supply that puts out 48v @ 12a, but also says it uses 11a at the wall. I can't imagine it's that inefficient, but that's how they rated it so it gets it's own 15a circuit (well, also a 100w light on that circuit) for what it's used for.