I have been happy with https://www.amazon.com/gp/product/B000NPT4TK/ as a desktop power supply for a small 2m/70cm mobile radio.

The MXT275 is advertised as being a 15 watt radio drawing 13.8 volts DC - to get amps, divide the power by the voltage, so it should require something in the neighborhood of 15/13.8 amps, or a little more than 1 amp.

The power consumption of the radio may be more than just its output - but even if you doubled that figure, even a relatively small power supply should be sufficient.

Another aspect to consider is the electrical connection - the power supply I linked above has two screw terminals that connect to two bare wires, while the MXT275 has a cigarette-lighter style 12V plug (which can be easily snipped off). If you prefer not to cut the plug off, you'll want to look for power supplies that provide a 12v socket. This might be a contender: https://www.amazon.com/dp/B0002BA570/ but I've never used it so .. ??

50 amps is serious overkill for this application.

I note that this page for the MXT275 https://www.crutchfield.com/S-A5hLcX0wabu/p_102MXT275/Midland-MicroMobile-MXT275.html says that it uses a 5 amp fuse, so that should tell you the upper limit of the potential power draw for the radio.

Looks like you're missing a few things to get it up and running. I'll link what I think you'll need below, and provide the cheapest/best stuff for an entry level rig.

You'll need a 12V power supply if you plan on running it from home as a "base". Here is one on Amazon for $31.00

https://www.amazon.com/dp/B0002BA570/ref=cm_sw_r_apa_i_GjrFEb2QEDQ4W

Not being able to see the power wire end, you may need a 12V cigarette adapter. Cut the wire, connect black to black, red to red, ideally soldering them and then using a heat shrink would be best, but cheap butt-connectors and electrical tape will suffice. Here is a 12V cigarette lighter plug on Amazon for $14.00

https://www.amazon.com/dp/B0016LG0CY/ref=cm_sw_r_apa_i_dprFEbRVC4YAQ

Your antenna seems to be incomplete as well. Consider buying a new, magnetic mount antenna. It includes the coax cable and is USUALLY pre-tuned for 11M (CB radio) out of the box. You SHOULD tune all radio/antenna pairs with a SWR meter, which I will discuss/link below, but in any case, here is a magnetic mount antenna on Amazon for $28

https://www.amazon.com/dp/B008ZDBM10/ref=cm_sw_r_apa_i_CtrFEbH7PH3BS

Now that you have your power supply, working radio, and antenna all hooked up, you should confirm proper SWR so that you don't damage your radio. I won't go into all the details about what SWR is or how to go about checking, but here is a link with all of that information for you to look into;

https://www.rightchannelradios.com/blogs/installation-guides/18428275-understanding-swr

Once you've got a grip on that, consider this SWR meter on Amazon for $22

https://www.amazon.com/dp/B002KRME3C/ref=cm_sw_r_apa_i_uzrFEb3DB7KGK

I hope this information helps you. Knowing what you have and what you need can be a daunting experience, especially if you are new to the hobby. This sub is very knowledgeable, as well as countless resources online. You should have little trouble in finding the information you need.

The Uniden 510XL is a fine little rig. While being entry level as far as equipment goes, it's reliable and user friendly, and fits in places you wouldn't believe! As someone who owns 2 of them currently, I highly advise a small external speaker for better audio. They are cheap and can be found anywhere. Here's one on Amazon for $17

https://www.amazon.com/dp/B000ZIC18Q/ref=cm_sw_r_apa_i_IDrFEbRTWHVFQ

As you develop in the hobby, you will learn a lot, not only about the equipment but radio theory as well. It's a very interesting subject, and with all the information and awesome equipment out there, it should provide you with years and years of fun!

Again, hope this all helps. If you have any questions, let me know or drop another post here in r/cbradio

See you on the waves!