This beefy 850W Corsair SF850L PSU is ideal for high power SFF PCs and marked down at Amazon
A high power PSU for less.
Snall form factor PC components can come at a bit of a premium, although with this current Amazon deal, you can get a beefy, reliable PSU designed specifically for smaller systems for a reasonable price, all things considered. This Corsair SF850L is efficient, offers a lot of power and comes bang-up-to-date with support for ATX 3.0 and 12VHPWR for £130, which is a price-match for Scan Computers from Amazon, so kudos.
850W of power is enough for running even some of the beefiest components available, being the minimum recommended wattage for more 'standard' RTX 4090s (such as the Founders Edition), while also being above the minimum recommendation for AMD's top of the line RX 7900 XTX. In fact, you get a little bit of headroom in going for an 850W option with AMD's top contender. If pairing this Corsair option with one of those cards, you'll just have to make sure the card has sufficient clearance to fit in your case, as some of them can be quite large to say the least. Of course, everything underneath that from both Nvidia and AMD will be more than adequate for this wattage.
The SF850L is also suitable for use with PCIe 5.0 and is an ATX 3.0 PSU, making it suitable for use with some of the latest components. In addition, it comes with a 12VHPWR connector, too, so you can run modern Nvidia GPUs without needing to purchase any other adapters or cables, which is especially useful. This is also a fully modular PSU, so you can save on some of the unneeded cable spaghetti when putting it in your system and connecting everything up. That's important anyway, but especially in an SFF system where you've got less space to manoeuvre.
This PSU is also a top-tier option on the Cultists PSU Tier List (formerly of the LTT Forums) by virtue of being one of Corsair's SF-L PSUs, while it's also 80+ Gold rated, which is testament to its excellent efficiency. Just in case you were wondering, the SFX-L form factor is still perfectly fine for small form factor PCs, but it is slightly larger than other SFX PSUs out there. You'll just want to check your case's supported sizes to be sure it'll fit okay.
If you want to grab a capable PSU for a high power, small form factor system, this Amazon reduction on the Corsair SF850L is not to be missed.