Just forget about the whole wattage thing for now. It’s really all about how many photons of light reach your plant, and what light spectrum (the “color”) of light is reaching the plant. I don’t want to make things too complicated with scientific mumbo-jumbo though. I’ll see if I can find a link to a beginners guide to horticultural lighting or something for you.
The Mars Hydro equivalent to the HLG 260 XL would be the TSL 2000, not the TSW. You’ll notice that it’s rectangular, like your closet. Mars Hydro is a little more of a discount lighting company. Their lights are decent, but a step below HLG. They use a slightly older (and thus cheaper) LED. It makes their lights less expensive but also less efficient. They will use a little more electricity, will make your closet a little warmer and less photons of light will reach your plants. BUT - if you can’t afford the HLG, then go for the Mars Hydro. It will still grow a very nice plant.
The Viparspectra light you mentioned is a great example of an “Amazon Lie” LED lamp. That is actually a 390 watt lamp, not 900. Also, take notice of the blue-purple color the light gives off. These lights you will see referred to around here as "blurple lights. Don’t bother with one of these lights unless you absolutely can’t afford a proper grow light. One of these will grow a plant, just not a bountiful one. Countless people have made that mistake, then later regretted it and spent money on a better light. So, it just becomes money wasted in the long run.