It should be noted that at this point in his chronology, Superman's natural powers were already MASSIVELY amped due to his exposure to Kryptonite X...When Henshaw attempted to kill Supes via blasting him with k-nite, Eradicator jumped in the way of the blast before it directly touched Supes(essentially sacrificing himself), and the bleed-over energies then passed into Superman. After this happened, Supes was not only returned to full power, but he felt better than ever:
https://i.imgur.com/A5Fc715.jpg
https://i.imgur.com/ZUOr1em.jpg
https://i.imgur.com/IMFlneF.jpg
https://i.imgur.com/PpaVx4Q.jpg
https://i.imgur.com/JqED6sp.jpg
https://i.imgur.com/TL1K0F7.jpg
https://i.imgur.com/jsqwvoo.jpg
https://i.imgur.com/8uYRKnL.jpg
"I'm rejuvenated in a way I never thought possible! Something tells me I'll be able to handle anything better than ever!"
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Soon thereafter(the same month/year the H/P arc began), it would be revealed that Superman had become immensely more powerful. Examples...
"Just tapped him a little... And he flew back like I hit him with my best haymaker!":
https://i.imgur.com/KgUftR4.jpg
"Even using as little effort as possible, I'm still stronger...faster...and more powerful than EVER before!":
https://i.imgur.com/vyiofCJ.jpg
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Superman's amp was then expanded on...
Hamilton: "You're absorbing solar radiation --and OTHER energies-- much faster than EVER before! This is because you've been irradiated by something vaguely familiar to Kryptonite -- call it Kryptonite-X."
Superman: "The last time I was exposed to Kryptonite, it passed through the Eradiactor first... Recharging my powers instantly!"
Hamilton: "A bit of foreshadowing there, I'd say. Bluntly, there's no physical way to expend your energy fast enough. Your powers will keep increasing until your body can't contain them.":
https://i.imgur.com/O04ni6h.jpg
https://i.imgur.com/kuppq8g.jpg
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Superman himself mentioned his increased power during the H/P arc(before he had even obtained a MotherBox)...
"I'm BETTER than before, too! STRONGER.":
https://i.imgur.com/DNjZeeh.jpg
______________________________________
His amplified power during the H/P-era was reinforced again here...
"After his recovery, [Superman] was stronger than EVER. Good thing, too -- 'cause Doomsday had cheated death as well! Even with the EXTRA power, he still needed some gizmo called a 'Mother Box' to HELP HIM stand up to Doomsday.":
https://i.imgur.com/xTntuCb.jpg
So as you can see- during the events of the H/P arc, Superman's natural abilities were hyper-amped to such an extent that he compared the power behind his LIGHTEST TAP to that of his BEST HAYMAKER before the amp.. And what was his BEST HAYMAKER previously? I'd say it was undoubtedly the final blow he used to 'kill' DoS Doomsday:
https://i.imgur.com/6dZAU4m.jpg
...Food for thought.
That being said, MotherBox sensed the threat H/P Doomsday posed, and amped/equipped Superman specifically to handle him. IOW, it was an AMP on top of Superman's existing AMP:
https://i.imgur.com/4RGKnUR.jpg
https://i.imgur.com/9SoKBzh.jpg
"MotherBox sensed the situation, and armed me for battle with Doomsday! [...] Hopefully I've caught up to Doomsday's next level of evolution!"
...Yet the amp it gleaned STILL wasn't remotely enough to contend with Doomsday, which is absolutely staggering given what MotherBox can do.