FYI you got very lucky because of the different 24 pin connector.
The ATX 4/8 pin and PCIe 6/8 pin are usually the same because let's be real here, there's not that many reasonable pinouts for half +12V, half GND (and 1/2 sense wires for the PCIe that everyone abuses for more power or just ignores completely) and even if they were different the only other option is a straight up short circuit. In that case any decent PSU will refuse to start and you should be safe. I wouldn't try it though.
However if you had been able to connect the wrong 24 pin cable then now your mobo, CPU and possibly GPU would also be dead.

PSU OEMs generally try to foolproof the cables for example by using 8 pin on the PSU side for the PCIe cables and 6 pin for the SATA/peripheral cables. However that doesn't prevent some people from shoving 6 pin connectors into 8 pin slots or using different cables (I know you just didn't want to recable everything).
The only OEM who seems to have figured out a solution is Super Flower. They use 9 pin connectors so their own cables will fit in any slot (and whatever pins aren't needed just aren't connected to the cable) and other cables won't fit at all.

I know that this doesn't help you at this point but someone else might read it and benefit.
The only thing that can help you now are backups.
I hope you've got backups.

They are not the same.
https://www.gamersnexus.net/guides/2702-psa-on-mixing-modular-psu-cables-dont-do-it

I'll give you a hint: Stuff caught fire.
So what do you think?

You can't, it doesn't utilize 4 threads properly.

Then everything is working fine.
Changing the GPU won't change fps in TF2 much. So either your problem existed with the 1050 Ti as well or there is no problem.
Up to means up to. Max with 4 cores active is 3.1 GHz. Working as intended.

Are your fps lower than with the 1050 Ti?
If they are the same then nothing is wrong.

If they are lower check the CPU temps, clockrate and utilization.

You just hooked up a PSU with a different pinout to the modular from a different manufacturer and killed your HDD.
I mean it caught fire.
What do you think happened to the SSD that use the same connectors?

If you're lucky only your HDD and SSDs are dead.

Which benchmarks?
The 8400 just doesn't make sense because the extra cores won't do anything, the 8100 is almost as fast and much cheaper and the 8350K is faster and cheaper even if you don't overclock it.

Either way things might change a bit until July.

Yeah none of that makes any sense.
You think you'll get more out of a 6 core in a game that doesn't even use 4.
You're paying extra for a Z mobo because you might by a K CPU later. When? In 3 months, so you just wasted 180$ on the i5-8400? In 3 years when new CPUs won't fit the socket and old CPUs that do aren't sold anymore?
Or even worse you're going to replace the 8400 with an 8700? Why?

Just for TF2 the 2400G iGPU is enough. Intel probably not (about 1/3 of the speed).
Keep in mind that a 1050 is "only" 65% faster than the 2400G too, so might not be worth it for 150$. If you plan on going with a dGPU right from the start you might as well save money and go for the 2200G (or whatever AMD's highest clocked 4 core ~100$ CPU is by the time you actually buy it) or the i3-8100 and a B360 mobo.

Or if you absolutely have to throw money at 10% more performance get the i3-8350K, a Z370 mobo and a dGPU.

And keep the SSD ffs.

#2836
There are no specific drivers. Same nVidia drivers for all GPUs.

#2837
Depends. Might be uncoolable depending on the voltage unless you delidd it.
Also http://www.teamfortress.tv/12714/pc-build-thread/?page=19#557

Both. Possibly weird form factor PSU.

So RAM, HDD and mobo should be fine if it's the tower version.
The case isn't that great, no idea about the PSU.
Overall ok for 150€. He might have to replace the case and PSU but it should be much cheaper than buying everything new.

Well what about the rest? Case, PSU, GPU (if there is any), SSD (maybe) and HDD?
If it's a large enough case and good PSU, decent RAM speed and already dual channel then literally the only thing he'd have to do is add/replace the GPU. Not bad for 150€.
If the case is too small, the mobo doesn't have a PCIe x16 slot, the RAM and PSU are shit then all he gets for 150€ is a used CPU that isn't even faster most of the time than a new 100€ CPU.

Portable as in a tablet?
And no, I don't care about those things.

That is completely wrong.

Fragmentation will still slow SSDs down. The difference is that an HDD is fast for sequential operations and basically unusable when you're doing random 4k while sequentially an SSD is faster than the "600MB/s" SATA III connection it's hooked up to and a bit slower or actually faster than the best case for an HDD even when you're doing terrible stuff.

The other things is that SSDs put data wherever the fuck they want to put it to minimize wear and defragment themselves in the background whenever they deem that necessary. They just tell you that the data is still at the same adress (lie, it moved) where you think you put it (lie, it was somewhere else from the start) because otherwise how would you ever find it?

It certainly turned into an experience for baud as well.
Juicy french drama.