Would a Corsair TX-M 550W Power Supply fit in my Dell Optiplex 3020 MT?

No because 3020 does not use standard power supply.

https://www.moddiy.com/products/Dell-OptiPlex-3020-PSU-Main-Power-24-Pin-to-8-Pin-Adapter-Cable-30cm.html

Bare minimum Recommended is EVGA 700BR.

https://www.bestbuy.com/site/evga-700w-atx12v-eps12v-80-plus-bronze-power-supply-dc-dc-technology-black/6346160.p?skuId=6346160

Any other recommendations? 

there are 2 answers,  what works now, or what you need next year, at next GPU upgrade.

or the RTX titan at 320watts just  it.

only you know what you need now and next year ,or as some do what they plan for 3 years, down the road.

why upgrade 3 times some say, but is  your choice.

cases in point, here. 8000 users with upgrades on this PC> LOOK see, and most have NEW PSU, not sold by DELL ever to go those fast 3D speeds,

this question has been covered on this forum  3020mT  + GPU or PSU vast times.

and ends the same way each time, did you search first>?  seems not, but IDK.

the answer is yes, and yes and yes,  with the ADAPTER , the MOBO HAS NO 24pin ATX power jack , oK?

yes many have ,yes it works and yes buy a 500 to 750watt PSU,  and the stock psu is 5.51" long and so are the ones presented, the sellers every one tell you what size the PSU is, ATX.

all are 86mm tall, ATX spec.

all are 150mm wide, ATX spec.

and they vary by length, 140mm for weak PSU and longer up to 160mm for 850watt at CORSAIR.

what PSU you buy is your call, ,vast are sold and you get  what you pay for, in quality.

Corsair TX-M 550W , at newegg shows length is ok I can not be Diety and speak for Newegg or Corsair not me, not anyone really, all you can do is read the spec, and BELIEVE it.  Go to Corsair.com and read, first, ok?

 Inches = MM divided by 25.4, (math)

please search here," 3020mt PSU"   this has been answered Vast time now,,,, endless for sure.

yes with the $7 adapter

I too have TX PSU.  and is very powerful. if your read the spec, huge power there even at 3v and 5v rails.

posted now vast times.

ok,  but playing top games runs the GPU clocks at max. 

at max the GPU goes to full power from the PSU<

that old dell PSU will overheat easy

that PC is not a gaming PC it is for business, like for email, or web cruise or running OFFICE and in 2D mode.

is was never designed to run any top AAA+ game ever.

there is nothing new here,  this is all normal,  now that I know what you are doing

VIDEO CARD: Nvidia GTX 660 or AMD Radeon HD 7870 equivalent DX11 GPU (best play)

but series 6 has no w10 support so GTX710 is now the new MIN. Nvidia rules, this. fact.

Your 1050ti only uses 75watts max, but your PSU is tiny,  150 for the PC and 75w for GPU is  225watts and your PSU gets hot, that is what it does and when it does the fan screams.  (BY DESIGN)

if you dont like noise get a 500 to 750w PSU. (for sure  TX or better PSU)

fortnite has endless settings, to change FPS, some can even lower the PSU load.  endless, fiddling there.

here is the card benchmarks just this game.

This is why i am buying a new PSU.My Stock 290w psu started making a lot of weird noises sience i got the Asus Gtx 1050 ti Cerberus 4gb OC.When playing Fortnite it's like i have a UFO in my Computer. IT'S SO LOUD.I can hear it through my headphones and it's so annoying.Even in standby i can hear my psu from 5 meters.So? Can it power my Graphics card (no extra cables required for external power) my cd drive, my ssd, my Hard Drive and my motherboard? And will this specific Model fit? If you want i can send you a recording so that you can hear the psu when i am playing fortnite.Thanks for replying! 

So i can Get THIS power supply or NOT? (the one i mentioned in the description) AND most importantly will it fit? 

old PSU are not good for gaming or new faster more powerful GPU cards.

old PSU have bad CAP/'S inside, old and weak (poor ESR) they are electrolytic capacitors)

the old PC will also make odd order Harmonic noises overloaded, or near max. new PSU have modern SMPS, 50kHz noise protections inside (heard as odd squealing sound on bad or old or failing PSU or Cheap PSUs)

next is the fan the fan spins fast to prevent melt down,.  if you use full  power on  any PSU made the Fans spin fast that is there job, just like you and your car, the too hot engine the fans spin faster, and for the same reasons.

all things made or even the sun, has  power loss,  (the latter is good, to grow food etc.)

All PSU made make usable power (for PC and GPU etc) and also has huge power loss 20% or more in the form of HEAT that must be expelled.

to make power (means convert  only) we must  burn and waste some power (means watts (P= VxA)

at 500watts  there is 100watt lost of heat, ever feel a 100w light bulb that huge hot heat (even burns a finger)?

this heat is in the PSU at many places transformers and those huge heatsinks inside, and if allowed to go too hot the PSU is damaged,  so the smart PSU spins the fans faster saving its own bacon. and make more noise doing so.

do you understand now what POWER is?  

The GPU card too runs its fan faster when too hot.

the CPU chip too runs its fan (bios does it) to cool the CPU and not let it overheat.

Heat is is the #1 cause of  short life of all electronics made. Now you know why fans work. and how.

A good rule of thumb might be.

Do a power budget, ?

150 watts for the PC, itself, then add GPU watts, next.  so if using a RTX2080 (random example) add 250watts more, is 400watts, but we need more for margin or dynamic current reasons,, I add 50% more, and that 600watt PSU. Note I am assuming a modern PSU with the NEW SINGLE RAIL +12vdc rail,   mine does 62 amps there.

and does  +3.3V@30A, +5V@30A, +12V@62A, -12V@0.8A, +5VSB@3.0A

750watt, but 650 is good too for sure....

your lil old 1050 needs only 75watts, so buy what you need now or later, your call all that.

and last old PSU for sure weak love to BSOD  the OS,  for sure gaming, for sure if lots of electronic noise on the RAILS.

also learn that a new PSU (correct) will only run the fans at over 275watts on 550watt max PSU, at 50% load.

so if noise really bothers you (IDK) buy a better PSU, based on that fact too.

good luck in your choices, buy from sources that allow exchanges and even upgrades same time.

I want to mention this point here, "all things made or even the sun, has power loss,  (the latter is good, to grow food etc.)" Just pick up the main thing you don't need to put efforts to make the things work correctly. Like we've been facing with a condition at best mouses for Fortnite and definitely the dell provides the best mouses in this regard.

Just want to mention that if you're facing issues with noise etc first check and then use.

@speedstep​ is the power supply you listed one that would work in an dell optiplex 3020?

Speedstep hasn't been on this forum for almost 2 years.

He wouldn't recommend a PSU that doesn't work.  Remember, you'll need the adapter cable that he also linked.