Okay, so I went with a 3m power cable replacement (this one). It uses a 6A plug so it should be able to power my PC. My main question is, can I safely use this with my Belkin extension cord while I've plugged in all the other devices? Estimates for peak wattage are xbox = 240W, macbook charger = 65W, 4k monitor = 50W. Total = 355W. Since the Belkin extension supports upto 1500W and is using a 6A socket, I should have enough wattage to power my PC safely (...right?).
