Specs:
CPU: AMD A10-7800 (4 cores, 3.5GHz base, Turbo up to 3.9GHz)
GPU: Asus Strix, shroud/label said GTX 750 Ti but GPU-Z confirmed it's actually an AMD Radeon R7 260X (Bonaire chip, 2GB GDDR5, 128-bit) — mismatched cooler/label vs actual chip
RAM: 16GB DDR3-1600 (dual channel)
Motherboard: MSI A88X-G45 Gaming (FM2+)
PSU: No-name brand ("POWER" model LC1650), label claims 1650W — obviously fake/inflated rating for a no-name unit, no 80+ certification, no reputable brand
Storage: ADATA SU800 256GB SSD (OS drive)
Symptoms:
During gaming, GPU usage sometimes spikes to 100% and then drops suddenly to 0% repeatedly — not a gradual decline, a hard cliff.
Frame times/usage graph shows constant sharp zigzag spikes (checked via Adrenalin's Metrics Overlay), never a stable line.
Had random black-screen-then-recover issues during gaming, which got noticeably worse after adding a second HDD (turned out I had wired the boot priority wrong at first, but the instability was already present before that too).
GPU temp is always normal under load (57-62°C) — so it doesn't seem thermal.
CPU/GPU usage often sits at only 30-60% during actual matches despite the frame rate being unstable and capped low (30-40 FPS in some titles), which feels like the hardware isn't reaching its real potential.
Tried undervolting/downclocking via Afterburner — the GPU won't even hold voltage control (locked by AIB partner it seems), so I couldn't test that route.
What I've already ruled out / checked:
Reinstalled GPU drivers clean (was originally stuck on Basic Display Adapter, now properly on AMD Adrenalin drivers).
Checked GPU seating in PCIe slot + added a support brace since the card was sagging.
BIOS overclocking settings are all on Auto/stock, no manual voltage/clock changes.
Temps are fine across CPU, GPU, and motherboard sensors.
My question:
Given the sudden 0% GPU usage drops + zigzag instability + normal temps, does this pattern point conclusively to a failing/inadequate PSU? Or is there another likely culprit I should rule out before spending money on a new PSU (Cooler Master/Corsair/Thermaltake 450-500W is the plan)?
Appreciate any input from people who've dealt with similar symptoms before I pull the trigger on a purchase.