In reference to the Power Supply Unit (PSU) query, it is essential to note that all PSUs should adhere to the ATX standard. However, certain PSU manufacturers extend the length, primarily in cases where higher wattage necessitates a larger PCB board. Consequently, the width and height dimensions remain fixed, with the variable factor being the length.
For a visual representation, please consult the product image of the HCS255 via the provided link. The PSU length in this case ranges from 175mm to 340mm (please note that this measurement is without the HDD tray). Your specific requirements and constraints may vary, and we encourage you to review the linked information thoroughly.