Power Supply
White<Bronze<Silver<Gold<Platinum<Titanium
In other words, white is the easiest certification to get, and most budget power supplies will be here or bronze. Again, for office computers, this is usually completely fine. Silver and gold are very efficient and are great for most gamers or users who want reliability. Platinum and Titanium are the best in efficiency and are usually designed to last an entire decade, or so their warranty would suggest.
Please note that there is nothing wrong with using a high wattage/highly rated power supply in a professional computer that won't be using too much electricity, other than the price increase from the more expensive power supply. However, using a low-wattage power supply with very demanding components is usually a bad idea and can lead to random shut downs or the system not powering on at all. We'll let you know if you picked a power supply that is too low to run your parts.