Grab this 850W Cooler Master SFX 80+ Gold PSU for £108 with an eBay code
Ideal for high-power SFF PCs.
If you're running a PC that's in a smaller form factor case, such as the lovely Fractal Terra or otherwise, then a full-size ATX PSU simply won't do. That's why we have SFX power supplies - however, these can come at a premium in comparison to their more 'standard' counterparts, which is what makes this reduction on an 850W Cooler Master SFX option. This PSU is normally priced at £125 (or £144 in the case of Tech Next Day on eBay), but by using the power of the ANNIVERSARY25 code from Tech Next Day's eBay store, you can get it for £108, which is rather solid.
This is a reliable 80+ Gold rated unit, which is is testament to its efficiency, and also provides peace of mind, too. The fact this is also a fully modular PSU also helps for cable management, and to allow for better airflow. Building a PC without a modular power supply can be a bit of a pain, given you'd have to find somewhere to put all the loose cables you aren't using, so a fully modular option keeps things convenient, especially in a smaller form factor case.
With this in mind, 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. I fact, you get a little bit of headroom in going for an 850W option with AMD's top contender. If pairing this Cooler Master 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, verything underneath that from both Nvidia and AMD will be more than adequate for this wattage.
What's also interesting here is that this Cooler Master option also comes with a bracket so it can fit in even bigger cases. That is, ones that support anything up to an oversized E-ATX motherboard, so if you decide that the small form factor life isn't for you down the line, and you want to retain your PSU, this Cooler Master one can slot right on. In addition, if it's any further testament to its reliablity and efficiency, Cooler Master back it with a 10 year warranty, and it's also A-tier rated on the Cultists PSU Tier List (formerly of LTT Forums).
If you want to grab a beefy PSU for small form factor PCs at quite a discount, this deal on the Cooler Master V850 from Tech Next Day on eBay is worth a look.