The power supply (PSU) is probably one of the most easy things to deal with for a PC. With a VTPO in mind the first most important thing is reliability and the second is quietness. The rest is a 'magic' box with cables coming out of it.
Firstly add up all of the power requirements for each component in your PC in Watts. If you don't have a figure for a particular component in Watts, then you can easily calculate it from two other parameters, Amps (I) and Volts (V). Amps multiplied by Volts = Watts or I x V = W. A simple mnemonic to help you remember is that well known lady IVy Watts.
Ensure that you add the figure for EACH power rail, i.e. 12v, 5v and sometimes -5v and don't forget to add the power for that humungous processor cooling fan you just acquired! I then add 10% as a sensible 'margin'. Then add another 10% for future expansion (maybe another hard drive) and then another 10% for anything that might be 'buss powered' such as a USB/MIDI interface or Firewire sound card. That will give you a sensible wattage figure to rate your power supply. Yes, 30% looks excessive, but we're looking for a major component that is not likely to shut down under load, and is unlikely to 'fry' your expensive motherboard! Remember that you may prefer to leave your VTPO PC permanently powered up, so that PSU has to run 24/7 and has to be ultra-reliable. Purchase a PSU made by a reputable manufacturer and don't be tempted to buy a 'cheapy' at a boot fair or use one from a mate's junk box.
PC 'noise' can be controlled well by a wise choice of case but there's no point in using noisy components in the first place, so again, choose your power supply from a range known to be QUIET and preferably with intelligent fan control. This will allow the PSU to intelligently link to the motherboard and only run the cooling fan/s at full speed when actually needed for cooling, thus keeping fan noise to a minimum. DO NOT EVER try to control a noisy fan by internal modification of the power supply. In fact DO NOT EVER attempt to open the case of any power supply. Apart from lethal voltages that 'lurk within', PSUs also contain components that could catch fire or explode if you happen to make the wrong 'correction' or inadvertently drop something inside. DON'T DO IT! Apart from invalidating the warranty you could die!!! If a PSU is noisy, return it to your supplier for repair or replacement. If it's out of warranty, consider 'binning' it and buy another one.
Lastly, ensure that your PSU choice can cater for all of the supply needs by way of the correct connectors for your motherboard, graphics card (some PCIe cards require an extra 12v supply) and anything else (such as extra fans) that take power. Ensure that the PSU supports all of the latest 'gizmos' that are on offer and may be part of your motherboard, and ensure that there are sufficient cables and connectors to reach all peripherals such as hard drives, which are often mounted in the opposite corner of the case to the PSU. Modular power supplies can help to make fitting easier, but consider the fact that with all of those plugs and sockets, there's a potential for fault development that's not there where cables are hard-wired.
Regardless of what's been written here and elsewhere, follow the manufacturer's instructions.