Any ways to fix slow powerline adapters? ( slower Wi-Fi speed then phone )?

So I just got the 300 megabits fiber internet installed few hours ago and it did work perfectly with high speed. It was good in my TV, tablets and iPhone but the only device that shockingly got low internet speed is my PC with a LAN cable connected (powerline adapter). It only gave me about 5.04 megabits yet it is still a wired conenction. I tried to made it connect the 5ghz Wi-Fi but the LAN name is under the 2.4ghz ones. Any idea how to make it connect to a 5ghz internet or fix the issue?

What is the rated speed of your power line adapters (Ethernet over electrical wiring)? The older models worked at a lower speed than current models.
Are you using any power conditioning/spike limiting adapters to protect your sensitive electrical items? If so, these can greater slow the transmission rate of the power line adapters.
Could it be that your mains electricity supply is noisy, with a lot of interference? If so, this will cause data errors meaning data has to be re-sent, slowing down the resulting bit rate.
Have you tried connecting an Ethernet cable directly from your PC to your new router (you would have needed a new router to use the fibre connection)? That should give you the fastest speed possible, faster than wireless.
Unless your PC is VERY old, its network card will be capable of at least 100 mbs. Most will be much faster so I doubt if the problem is in your PC.

Powerline network adapters must be connected on the same phase of the mains supply, and must be fed from the same electricity meter. Ideally, they will be on the same circuit from the main distribution board, so that the power outlets are fed from the same fuse or breaker, although They will work on different fuses/breakers providing it is the same phase and meter.

If you have a surge suppressor feeding your PC, the Powerline adapter must be on the wall outlet side of the suppressor. The same applies to the one connected to the router. The Ethernet cable from the adapter to the PC will have high surge resistance built in to the Ethernet transceivers at each end, so although a voltage spike might damage the Powerline adapter, a surge suppressor between the outlet for the adapter and the PC will still protect the PC properly.

Although different makes and speeds of adapters will work together, except for the very old adapters that offered 85 Mbps or less, it is normally better to use adapters of the same make and speed together.

It helps with a question like this if you had included the make and model of the Powerline adapters. If anyone has experienced problems with the specific adapters you are using, they can offer advice more readily.

Others have told you about the "power line" adapters… Like many other things not all power line adapters are built to be high speed! Many older units don't supply much more speed.
However, you also asked how to connect to 5 gig Wi-Fi.
First if all you see on the available networks is the 2.4 SSID your adapter probably does not have both frequencies! Many cards are single band cards. You need an adapter on your machine that is "DUAL BAND". Buying a dual band USB adapter is the easy fix for the issue. Simply plug into your usb port, add the drivers, connect to your 5 gig Wi-Fi! The other option is to replace the internal 2.4 gig card with a dual band adapter. (May be easy, may not be. It depends on the unit itself.)

Just try different outlets for both the router powerline adapter and the powerline adapter connecting to your pc. If you have exhausted all the outlet combinations near the pc and router, then you're SOL.

You will have to use a long ethernet cable from the router, or you will need to use Wi-Fi. To use 5ghz Wi-Fi, both the router itself and the wireless adapter connected to pc need to support it.

If using Wi-Fi on your PC, id recommend this adapter https://www.amazon.com/...B00F42V83C
The ones with more transmit and receive antennas (often labeled as 3T3R or 3x3 or 4T4R or 4x4) are what you want to look for, to get the best Wi-Fi signal stability. The number of antenna doesn't always mean that, as you can have 4 or 6 antennas running in a 2x2 config, which is just a 2x2. Personally, i have the adapter linked above (bought it used for $45) and it works really good. Can even play games on Wi-Fi really well.

"… Low internet speed is my PC with a LAN cable connected (powerline adapter)… Yet it is still a wired conenction… "
-- NO. A God Damned powerline adapter is ** NOT ** a wired connection.

I have been in telecommunication since 1966, was a top tech. If you want a solid connection, you want wire. If you do not want troubles, run an Ethernet cable from the router to your PC. And don't try to tell me that you can't. I have never been unable to run an Ethernet cable. I could show you, if you give me more information.

That is correct. Your Powerline adapters are probably rated at 150mbs and are not Gigabit. Hence you'll need to upgrade them to faster ones to take advantage of the greater speed.

Else get a decent Wi-Fi card for your PC