./facepalm @ Christmas comments.
You cannot simply "convert" a 120v circuit into a 220v circuit. once you move the neutral to a different phase hot, everything else on that circuit, all the other lamps, receptacles, and any other device is now being fed 220v. More than that, the reason they want you on a 220v circuit for "OC mode" is because at 1500w/120v, you are pushing the 80% safety rating of most 15A bedroom/office circuits (12A). If you installed a step up transformer on your 120v circuit to get 220v (this is a ridiculous idea, BTW), you'd still be
pulling the same current from the 120v circuit AND adding in your transformer losses into it, likely further overloading the circuit. This situation is even more complicated by the distance between your PC and the panel, as well as poor back-stab wiring done in most homes. The losses along the way are cumulative. Once you load up a 15A circuit, you will notice the voltage dropping on that circuit. As the voltage drops, your PSU will pull even more current to maintain the same output power. If you are on the end of the circuit and you load it up, you can goto the other receptacles on that circuit and feel them heat up, which btw further increases resistance, causes voltage drop, and increases current load.
If you live in an older home that hasn't had the receptacles serviced by a good electrician, you are likely to severely endanger your home by running 1500w+ out of your office/bedroom. Uninformed users just take for granted that the power is there, and as long as it doesn't pop a fuse/breaker that everything is ok. Well, it's not.
Electricity is no joke. I did some work in this older 1960's home that had long runs across the house and baseboard heaters everywhere. When we pulled down the fiberglass insulation to run new circuits, the foil had bonded to the romex (electrical wire) insulation sheath. There were black burn marks over most of the wires, following the hot inside the sheath. The electrician that installed the wire sized it properly for the load, but did not derate it for the distance he was running. This very well could have caught their house on fire.
You are far better off running a single dedicated 20A/120v circuit for your PC to use. That's 1920w you can safely use without heating the wire up. Don't think you can just change the breaker either. It needs to be run with #12, or #10 (if derated). You should only consider 220v in the instance that you need to run multiple high draw machines on a single dedicated circuit. You'd have to get special cables, and if you want a UPS they get pretty darned expensive at 220v.
Don't expect it to be cheap, but if you do have a new circuit run, ask them to use 3 wire for 2 circuits. For a marginal increase in the cost of the wire (one extra conductor) plus a second breaker, you can get two dedicated 20A circuits in the same place. The labor difference is minimal, as most of the labor is in running the wire itself, which is the same. We call them quads, as they are usually installed in 2 gang metal utility boxes, with 2 receptacles each on a different circuit. This is popular in garages and work benches where you need to run multiple pieces of equipment at the same time.
Good luck.
