Can I check how many power can my mother board provide? I don't know how to.
They're typically not stated anywhere, not even in the manual. They just do the typical "can power up to 600ohm headphones," which in some cases is like slapping on a 2.2L I4 engine into a pick up truck with short gearing to make it seem zippy but put a trailer with a racing bike on that truck and four people in the cab and it'll be as fast and nimble as a mail delivery van.
I can't find any info of my motherboard lol
You can open your tower and look on the motherboard then Google its model number. It's somewhere near the chipset heatsink, but in many cases the graphics card will hide it so you need to pull that out.
Still, output power specs even on boards that claim to have good amp circuits are typically not stated. One can guess a ballpark figure based on other amps that have the same type and number of op-amps, and then conservatively guess it will be below that figure considering the motherboard engineers' forte isn't amps and the mobo isn't working with a dedicated PSU for the audio section, even with giant caps inside your PSU there's still the graphics card working off of it.
Maybe I'll just buy the uber version. Do I need to buy some kind of better cable for USB and rca? Or just getting a normal one as a entry.
Get Schiit PYST or order from BlueJeans Cable.
If you're getting the Uber though why use USB? Check whether your motherboard has SPDIF toslink or coax and use that. The Modi2 Uber comes with its own power brick so it's not dependent on USB power either. The only way USB is better is if you need a compact USB-powered DAC-HPamp or you're using DSD, which typically needs the bandwidth of USB/HDMI/Firewire/etc.
The price is acceptable and they have both USB and rca cable. Is it produce better sound quality than the normal cheap one?
Unless you're comparing them to the really cheap RCA cables that come bundled with mega store optical video disc players, no. And even then I can't guess if the difference is audible to you.
Build quality is better though and the PYST RCA and XLR are short cables designed specifically for used with stacked Schiit gear, so you have less cable clutter.