Modern PCs are power-hungry machines. High-end GPUs like the RTX 5080 alone have a TGP (total graphics power) of 360W, raising the minimum requirement for PSUs in high-end systems to a minimum of 850W, as Nvidia advises. However, these GPUs aren't the only power-hungry components in your system. For the CPU, it seems like it would barely sip power, but that's not true for newer processors.
Looking at a CPU spec sheet, TDP alone does not tell the whole story because, in reality, the processor might even draw twice that power during peak activity. So, if you're planning a new build soon, keep an eye on the CPU's Maximum Turbo Power draw, which can be much higher than TDP, and avoid making the wrong purchase decisions for the rest of your components.
TDP describes sustained load, not peak draw
The Core i9-14900K is rated at 125W but is specified to pull 253W
A CPU has different power states it can operate in. For Intel CPUs, TDP is the base power that the processor consumes under a sustained workload, also called Processor Base Power (PL1). However, clocks can sometimes rise, and the CPU will boost under heavy workloads, reaching boost clocks and drawing even more power, called Maximum Turbo Power, or PL2.
At higher speeds, though, the power draw increases substantially because higher clock speeds need more voltage. For instance, Intel's Core i9 14900K has a PL1 of 125W, but at PL2 the spec sheet lists a whopping 253W draw, even though it's time-limited.
PL1 is labeled as TDP, so buyers confuse it with the maximum power draw. However, TDP applies only to PL1, so you shouldn't base a PC build solely on it, because a CPU can draw twice as much power under PL2.
AMD uses different naming conventions. TDP is the equivalent of Intel's PL1, while PPT (Package Power Tracking) is the PL2 equivalent; on AM5, PPT draws about 1.35x TDP, which is much less than Intel's.
How PL2 and Tau set the boost limit
Motherboard firmware can stretch both well past the manufacturer's defaults
By default, a CPU runs under the PL1 limit unless it needs more performance, in which case PL2 kicks in.
However, these boost speeds don't last long because, at a higher power, the processor becomes hotter, and that's when Tau drops because thermal throttling becomes a concern; otherwise, it's a phenomenon where performance starts to deteriorate as the CPU automatically slows itself down to prevent permanent damage.
PL2 depends on the CPU's Tau, a time window intended to reach the higher power draw, calculated in seconds before it drops back to PL1. The interesting part is that PL2 can vary across motherboards because of firmware limits, even if the manufacturer specifies different values.
For instance, a motherboard manufacturer may extend the Tau window to squeeze more performance out of the CPU for marketing purposes.
What this means for your next PC purchase
Size your PSU, cooler, and board for PL2
Credit: Dave Meikleham \ MakeUseOf
The most important part of building a PC is choosing the right PSU, and if you plan on upgrading or buying a new PC anytime soon, I recommend getting a PSU with an adequate supply, keeping the CPU and GPU's peak draws in mind, so the PC doesn't become unstable or damage the components if it fails to provide the required power.
The PSU shouldn't be the only concern, though. Cooling plays an equal part in ensuring your PC performs efficiently. A budget cooler won't cut it for a high-end CPU requiring a PL2 power draw of 253W like the Core i9 14900K.
You will probably have to get a cooler (preferably AIO) rated for 250W or more, not the PL1 limit. With insufficient cooling, the CPU will likely thermal throttle, failing to provide the advertised performance.
Motherboards also matter just as much as the PSU and cooling. Cheaper boards usually have fewer heatsinks and weaker VRMs to make up for the reduced costs.
Pairing a weak board with a high-end CPU can lower performance if the motherboard struggles to keep temperatures down because weaker VRMs throttle the processor. Check the VRMs and heatsink design of any motherboard before deciding to pair it with a K-series chip.
Plan your next build around peak power
Accounting for the GPU, CPU, RAM, and other components and the RGB fans on your PC, even a mid-end PC build requires around 750–800W of power. For any PC purchase, leave a headroom of at least 20–30% more watts than the combined peak, even after accounting for the highest power your PC can consume.
The reason is that PSUs don't perform at their peak all the time, and some of the power is lost during the conversion of AC to DC as heat. An undersized PSU with no headroom wouldn't be able to hold steady voltages after a while, in which case the system may start to crash and randomly shut down at peak consumption.