more or less as it is stated... is there a ruling regarding power armor, since the armor is , well powered?

Or is it mostly power 'assist' armor, as in, you still have to be massively strong to utilize it?

Its own weight definitely doesn't count. Ascension has rules for unpowered power armour - you need to make a -60 str test to be able to move.

Short answer, no the armor's weight doesn't count against your limit. It doesn't mention this is the DH rulebook, but the Rogue Trader book is imminently clear about this. It in fact elaborates very well on the power armor rules.

Quoted for your Convenience (Rogue Trader Core Rulebook pg. 139)

"For all types of Power Armor, the weight of the armor does not count for calculating the wearer's normal carrying limit."

Furthermore, in Ascension (Pg 144)

"... one wearing power armor can move and fight as if he was unencumbered, his suit's augmetic systems compensating entirely for the armor's crushing weight and bulk."

Rogue Trader's rules are perfectly serviceable for DH, at least where Dark Heresy fails to cover the basics. Most GMs consider them perfectly interchangeable. And the Ascension text is also pretty dang clear.