PSU Sizing in BuildSmith: The Check That Stops the Mid-Generation Restart
The part that kills more first builds than any other is the power supply, usually discovered when the machine restarts mid generation. BuildSmith treats PSU sizing as a check, not a guess: it adds the TDP figures of your GPU and CPU from the directory data, applies headroom for transient spikes, and flags any PSU in the plan that falls short.
The headroom is the honest part. A modern flagship card can spike well past its rated TDP for milliseconds, and a supply sized exactly to the spec sheet is a supply sized to crash. The rule the app applies, card TDP times 1.4 plus 150 W for the rest of the system, lands most single GPU builds one tier above the naive answer, which matches what experienced builders do by instinct.
What the check sees: top consumer cards by TDP
| GPU | VRAM | Rated TDP | PSU class the check asks for |
|---|---|---|---|
| NVIDIA GeForce RTX 5090 | 32 GB | 575 W | 955 W class |
| ASUS ROG Astral GeForce RTX 5090 | 32 GB | 575 W | 955 W class |
| MSI Suprim X GeForce RTX 5090 | 32 GB | 575 W | 955 W class |
| Gigabyte AORUS Master GeForce RTX 5090 | 32 GB | 575 W | 955 W class |
| Zotac AMP Extreme Infinity GeForce RTX 5090 | 32 GB | 575 W | 955 W class |
| PNY Epic-X RGB OC GeForce RTX 5090 | 32 GB | 575 W | 955 W class |
| Palit GameRock OC GeForce RTX 5090 | 32 GB | 575 W | 955 W class |
| ASUS ProArt GeForce RTX 5090 OC | 32 GB | 575 W | 955 W class |
| NVIDIA GeForce RTX 4090 | 24 GB | 450 W | 780 W class |
| NVIDIA GeForce RTX 3090 Ti | 24 GB | 450 W | 780 W class |
Rated TDP at the top of the consumer range
Multi GPU plans get the strict version: the app sums every card, refuses to bless a dual 5090 plan on anything under the 1600 W class entries in the directory, and says so in plain language instead of letting the cart check out. It is a small feature and it is the one testers thank us for.
The check also runs in reverse when you already own a supply. Tell the planner the PSU in your current machine and it caps the GPU tier it will recommend, instead of planning a dream build your wiring cannot feed. A surprising number of upgrade plans get more honest the moment that one field is filled in, and more than a few flagship card ambitions have quietly become 4070 class plans at exactly that step.
BuildSmith is in development. The PSU category page has the supplies it checks against, and the waitlist is on the homepage.