The I-192 is for nonimmigrant status like the U, whereas the I-601 is to waive a ground of inadmissibiliy when adjusting status to legal permanent resident. Nonimmigrant status is a visa of limited duration without permanency, while the immigrant visa intention is to live permanently in the US. The U is a hybrid as it allows adjustment of status after year 3. But like most other nonimmigrant visas it expires and is not permanent. Have your attorney explain this to you. I do not advise you to do this on your own. It's very technical. The I-918 sup B sign by law enforcement must contain the correct language. If denied, you may not be able to reapply. There are many non profits that are low or no fee. This is too important to do yourself.
U do not use I 601 form for a U visa related waiver. Use I192 but do it with an attorney
NYC EXPERIENCED IMMIGRATION ATTORNEYS www.myattorneyusa.com; email: firstname.lastname@example.org; Phone: (866) 456-8654; Fax: 212-964-0440; Cell: 212-202-0325. The information contained in this answer is provided for informational purposes only, and should not be construed as legal advice on any subject matter.
The I-192 is much more forgiving than the I-601 and easier to obtain, especially for U visa applicants. The I-601 is usually tied to proving a US citizen/LPR spouse or parent (or sometimes child) is going to suffer extreme hardship if the I-601 is not approved. There's no need to prove extreme hardship for the I-192. The I-192 also forgives grounds of inadmissibility that are not forgiven by the I-601.