A system administrator is sizing a replacement power supply unit (PSU) for a CAD workstati… — CompTIA A+ (Core 1 & Core 2)

A system administrator is sizing a replacement power supply unit (PSU) for a CAD workstation. The internal components have the following continuous power specifications:

- CPU: $105\text{ W}$
- PCIe Graphics Card: $280\text{ W}$
- PCIe Sound & Capture Cards: $35\text{ W}$ total
- Motherboard, RAM, and Storage Drives: $40\text{ W}$ total

To account for brief GPU transient power excursions, a $35\%$ power overhead must be applied specifically to the graphics card TDP. Additionally, to ensure hardware longevity and system stability, the final total system peak draw must not exceed $80\%$ of the power supply's rated capacity (requiring a $20\%$ safety headroom margin).

What is the minimum recommended PSU wattage rating required for this workstation?

$700\text{ W}$ Answer
B
$600\text{ W}$
C
$500\text{ W}$
D
$460\text{ W}$

Answer

The minimum recommended PSU wattage rating is

700\text{ W}

The correct option (

700\text{ W}

) properly factors in the GPU's

35\%

transient power spike (

280\text{ W} \times 1.35 = 378\text{ W}

), resulting in a combined peak system draw of

558\text{ W}

. Accounting for the mandated

20\%

safety headroom margin (

558 / 0.80 = 697.5\text{ W}

) dictates selecting at least a

700\text{ W}

rated power supply unit.

Step-by-Step Solution

Calculate the adjusted peak draw for the GPU including the 35% transient allowance.

\text{Adjusted GPU Power} = 280\text{ W} \times 1.35 = 378\text{ W}

Modern graphics cards exhibit short-duration power spikes above their rated TDP during intensive workloads.

Sum all system component power draws to determine the total peak power requirement.

\text{Total Peak Power} = 105\text{ W} \text{ (CPU)} + 378\text{ W} \text{ (GPU)} + 35\text{ W} \text{ (Expansion Cards)} + 40\text{ W} \text{ (System)} = 558\text{ W}

All components draw from the power supply simultaneously during peak operational load.

Apply the 20% safety headroom margin requirement (total load

\le 80\%

of PSU capacity).

\text{Minimum Required PSU Capacity} = \frac{558\text{ W}}{0.80} = 697.5\text{ W}

Operating a PSU below 80% capacity prevents thermal degradation, avoids unexpected shutdowns, and maximizes power conversion efficiency.

Select the next available standard commercial PSU wattage rating.

Select

700\text{ W}

PSU (or

750\text{ W}

700\text{ W}

is unavailable).

Power supplies are manufactured in discrete wattage tiers.

Key Concept

Power Supply Unit (PSU) sizing, component TDP summation, GPU transient spike allowances, and safety headroom margins.

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