Microsecond-long all-atom molecular dynamics (MD) simulations and circular dichroism, laser Doppler velocimetry, and dynamic light scattering techniques have been used to investigate pH-induced changes in the secondary structure, charge, and conformation of poly-l-lysine (PLL) and poly-l-glutamic acid (PGA). The employed combination of the experimental methods reveals for both PLL and PGA a narrow pH range at which they are charged enough to form stable colloidal suspensions, maintaining their α-helix content above 60%; an elevated charge state of the peptides required for colloidal stability promotes the peptide solvation as a random coil. To obtain more microscopic view on the conformations and to verify the modelling performance, peptide secondary structure and conformations rising in MD simulations are also examined using three different force fields, i.e., OPLS-AA, CHARMM27, and AMBER99SB*-ILDNP. Ramachandran plots reveal that in the examined setup the α-helix content is systematically overestimated in CHARMM27, while OPLS-AA overestimate the β-sheet fraction at lower ionisation degrees. At high ionization degrees, the OPLS-AA force field predicted secondary structure fractions match the experimentally measured distribution most closely. However, the pH-induced changes in PLL and PGA secondary structure are reasonably captured only by the AMBER99SB*-ILDNP force field, with the exception of the fully charged PGA in which the α-helix content is overestimated. The comparison to simulations results shows that the examined force fields involve significant deviations in their predictions for charged homopolypeptides. The detailed mapping of secondary structure dependency on pH for the polypeptides, and especially the finding of stable colloidal α-helical regime for both examined peptides has significant potential for the practical applications of the charged homopolypeptides. The findings raise attention especially to the pH fine-tuning as underappreciated control factor in surface modification and self-assembly.