The power supply is the one part of a PC that can take everything else down with it, yet it is usually the last thing people budget for. Buy too small and the system crashes under load; buy a no-name unit and you risk the GPU; buy a 1,200W monster for an office PC and you have paid for capacity you will never use.
Here is a practical sizing method, an explanation of the labels, and six units from our shelves matched to common builds.
Step 1: Add up what your parts draw
Every component has a published power figure. Add them up, then leave headroom.
- CPU: use the manufacturer's maximum turbo power, not the base TDP. Mainstream desktop chips land between 65W and 250W.
- Graphics card: the single biggest number. Entry cards draw 75 to 150W, mid-range 200 to 300W, flagship cards 350 to 450W or more.
- Everything else: allow roughly 50 to 100W for motherboard, RAM, SSDs, fans and USB devices.
Example: a 125W CPU plus a 250W GPU plus 80W for the rest is 455W. That system is happy on a quality 650W unit and has room for a GPU upgrade on 750W.
Step 2: Why you want 20 to 40 percent headroom
Three reasons. Power supplies are most efficient and quietest around 50 to 70 percent load. Modern GPUs produce short power spikes well above their rated draw. And a PSU you buy today should survive at least one GPU upgrade. So take your total, divide by roughly 0.7, and round up to the nearest common size: 550, 650, 750 or 850W.
Step 3: Decode the labels
80 Plus efficiency ratings
80 Plus White, Bronze, Gold, Platinum and Titanium certify how much wall power becomes usable DC power at various loads. Bronze units are typically about 85 percent efficient at half load; Gold around 90 percent. The gap on your hydro bill is small for a PC used a few hours a day, but Gold units usually run cooler and quieter, which is why they cost more.
ATX 3.1 and PCIe 5.1 (the 12V-2x6 connector)
Current graphics cards increasingly use a single 16-pin 12V-2x6 connector instead of several 8-pin plugs. Units labelled ATX 3.1 / PCIe 5.1, like the Corsair CX650M, CX750M and the MSI MAG A850GL, include that cable natively and are designed to handle the transient spikes those cards create. If you are buying a new GPU, this label is worth prioritising.
Modular, semi-modular, non-modular
Non-modular units have every cable permanently attached: cheapest, but you stuff the unused cables behind the motherboard tray. Semi-modular units hard-wire the essential motherboard and CPU cables and let you add only the drive and GPU cables you need. Fully modular units detach everything. In a compact case, modularity is a genuine quality-of-life upgrade.
Six power supplies compared
| Product | Key specs (from the listing) | Price (CAD) | Who it's for |
|---|---|---|---|
|
Thermaltake Smart 500W 80+ White PSU PS-SPD-0500NPCWUS-W, 120mm Cooling Fan, Active PFC rated 4.5/5 by 10,700 buyers |
500W, 80+ White certified, 120mm cooling fan, active PFC | $90.99 | Office builds and entry GPUs with no overclocking. |
|
MSI MAG A550BN Non-Modular Compact 550W Power Supply, 80+ Bronze, Low-Noise Fan, Active PFC rated 4.7/5 by 1,500 buyers |
550W, 80+ Bronze, non-modular, compact, low-noise fan, active PFC | $112.99 | Budget gaming builds with a mainstream card. |
|
MSI MAG A650BN Non-Modular Compact 650W Power Supply, 80+ Bronze, Low-Noise Fan, Active PFC rated 4.6/5 by 4,200 buyers |
650W, 80+ Bronze, non-modular, compact, low-noise fan, active PFC | $120.99 | Mid-range gaming PCs that want headroom without the modular premium. |
| CORSAIR CX650M Semi-Modular ATX 3.1 Power Supply, 650W, PCIe 5.1, Low-Noise, Black | 650W, semi-modular, ATX 3.1, PCIe 5.1 connector, low-noise | $120.99 | New builds with a current-generation GPU that uses the 12V-2x6 connector. |
| CORSAIR CX750M Semi-Modular ATX 3.1 Power Supply, 750W, PCIe 5.1, Low-Noise, Black | 750W, semi-modular, ATX 3.1, PCIe 5.1, low-noise | $150.99 | Upper mid-range systems and anyone planning a GPU upgrade next year. |
|
MSI MAG A850GL Fully Modular Compact Gaming 850W Power Supply, 80+ Gold, ATX 3.1, PCIe 5.1 rated 4.5/5 by 2,000 buyers |
850W, 80+ Gold, fully modular, compact, ATX 3.1, PCIe 5.1 | $225.99 | High-end gaming and creator rigs where efficiency and clean cabling matter. |
Who each one is for
- Thermaltake Smart 500W 80+ White PSU PS-SPD-0500NPCWUS-W, 120mm Cooling Fan, Active PFC — Office builds and entry GPUs with no overclocking.
- MSI MAG A550BN Non-Modular Compact 550W Power Supply, 80+ Bronze, Low-Noise Fan, Active PFC — Budget gaming builds with a mainstream card.
- MSI MAG A650BN Non-Modular Compact 650W Power Supply, 80+ Bronze, Low-Noise Fan, Active PFC — Mid-range gaming PCs that want headroom without the modular premium.
- CORSAIR CX650M Semi-Modular ATX 3.1 Power Supply, 650W, PCIe 5.1, Low-Noise, Black — New builds with a current-generation GPU that uses the 12V-2x6 connector.
- CORSAIR CX750M Semi-Modular ATX 3.1 Power Supply, 750W, PCIe 5.1, Low-Noise, Black — Upper mid-range systems and anyone planning a GPU upgrade next year.
- MSI MAG A850GL Fully Modular Compact Gaming 850W Power Supply, 80+ Gold, ATX 3.1, PCIe 5.1 — High-end gaming and creator rigs where efficiency and clean cabling matter.
Buying checklist
- Add up CPU max turbo power + GPU board power + 80W, then divide by 0.7 and round up.
- Buying a new GPU? Prefer ATX 3.1 / PCIe 5.1 units with a native 12V-2x6 cable.
- Compact or windowed case? Semi- or fully modular keeps airflow clear.
- Check the physical length: compact PSUs fit small cases better.
- Count the SATA and PCIe connectors against your drives and GPU.
- Look for active PFC and a low-noise fan if the PC lives on your desk.
- Never daisy-chain a single PCIe cable to a high-power GPU if the card asks for separate cables.
FAQs
Is a bigger PSU wasteful?
A PSU only draws what the parts ask for, so an 850W unit running a 400W system does not burn 850W. The only waste is the purchase price.
Can I reuse my old PSU with a new GPU?
If it has enough wattage and the right connectors, yes. Cards using the 12V-2x6 plug usually include an adapter, but a native cable from an ATX 3.1 unit is cleaner and safer.
Do I need 80 Plus Gold?
Not strictly. Bronze units like the MSI MAG A550BN and A650BN are reliable for mainstream builds. Gold earns its premium on systems that run many hours a day or where noise matters.
What is active PFC?
Power factor correction circuitry that keeps the unit drawing current cleanly from the wall. All modern quality units, including every one listed here, have it.
Semi-modular or fully modular?
Semi-modular saves money and still removes the clutter of unused drive cables. Fully modular is nicest for custom cable kits and tiny cases.
Ready to upgrade?
Browse the full PC Components collection at Nova Toronto Electronics. We ship Canada-wide from Milton, Ontario: flat $7.95 shipping, free on orders over $79, and every order is covered by our 30-day return policy. Prices are in Canadian dollars before HST, so what you see is what a Canadian pays — no surprise duties or currency conversion.